The obvious answer is because the environmental movement is intrinsically revolutionary and requiring of something along the lines of a participatory economy.
Wikipedia explains environmentalists this way
Environmentalists advocate the sustainable management of resources and stewardship of the environment through changes in public policy and individual behavior.
That is actually a good definition, but why do we advocate the sustainable management of resources and stewardship of the environment? What information is impregnated in that question?
For starters, we are destroying entire ecosystems. In just over half a century we have reduced our planets wetlands, grasslands and rain forests by half and since the Industrial Revolution we have kicked off a climate change that is probably the biggest danger we face. We have steadily been dumping toxins into our air, soil and water supplies. For a long time we saw Nature as an enemy or a source of infinite resources. We know now that not only is it finite but it is fragile. Slight disruptions in biodiversity can create a chain effect that can wipe out entire species, including humans.
E.O. Wilson, eat your heart out!
And just how is sustainable management and stewardship of the environment revolutionary? What precisely do I mean by revolution? Just like the sciences or politics, a revolution is a new system that replaces an old one. In other words, the existing system of political and economic order is becoming obsolete and if we want to be around to see it replaced we need a revolution - that is we need a new way of conducting our economies and polities. Otherwise this precipice we are standing on may crumble under our feet (possibly due to soil erosion!) and see us falling off a steep cliff (which used to be a mountain but whose top was blown off!).
This is what we need to start understanding: Disrupting coal-powered power plants or whaling boats near the shores of Japan and other tactics of civil disobedience are needed, but not enough. It's not enough to bring attention to a cause or to halt polluters. Greenpeace, you are amazing. We all appreciate your work. However, we also must have something to replace prevailing systems with. Robin Hahnel, co-creator of the economic alternative Participatory Economics, says this about the topic
The participatory planning procedure protects the environment in the following way. Federations of all those affected by a particular kind of pollutant are empowered in the participatory planning process to limit emissions to levels they deem desirable. A major liability of market economies is that because pollution adversely affects those who are "external" to the market transaction, market economies permit much more pollution than is efficient. The participatory planning procedure, on the other hand, guarantees that pollution will never be permitted unless those adversely affected feel that the positive effects of permitting an activity that generates pollution as a byproduct outweigh the negative effects of the pollution on themselves and the environment. Moreover, the participatory planning procedure generates reliable quantitative estimates of the costs of pollution and the benefits of environmental protection through the same procedures that it generates reliable estimates of the opportunity costs of using scarce resources and the social costs of producing different goods and services.
There is a cost and benefit to using natural resources. The cost may be pollution or depletion of resources or high cancer rates or extinct species or collapsing ecosystems, and the benefits may be the production and consumption of valued goods and services or better health. Under Capitalism the benefits may be present in transactions but the costs are not. Robin Hahnel explains again
The fact that a participatory economy can treat pollution and environmental preservation in an "incentive compatible" way is crucial. When producers or consumers have incentives to ignore damaging effects on the environment of their choices about what and how to produce and consume, it is not incentive compatible. And when polluters and pollution victims lack incentives to reveal the true costs of pollution to victims, or the true benefits of pollution to consumers of the products produced jointly with the pollution, it is not incentive compatible. But in a participatory economy since producers are charged for harmful emissions the damage from pollution is included in the cost of a worker council proposal -- giving producers just as much incentive to reduce pollution as any other cost of production. And since the indicative prices consumers are charged for goods in participatory planning include the costs of pollution associated with their production and consumption, there is just as much incentive for consumers to reduce consumption of goods that cause pollution as there is for them to reduce consumption of goods that require scarce productive resources or unpleasant labor to produce.
We cannot have zero pollution. We will have to accept some level of pollution or use of resources. The issue is how best to manage it in a sustainable way not only for us but for future generations. To do this we must calculate accurate prices that reflect the true social and environmental costs/benefits of production and consumption. We need this in order to gauge whether we are producing/consuming too much or too little. Two of the most important things we need to accomplish this are: (1) to give all those affected a meaningful and participatory way of effecting decisions and (2) to have an incentive for them to tell the truth.
Private enterprise allocated through market systems cannot give this since owners are motivated to maximize gains, which will drive them to exclude external costs and cut corners anywhere possible, and buyers want to devalue the goods so as to reduce their spending. Private enterprise and markets also don't provide an appropriate forum for those affected to have a say in decisions that affect them because if they did then they wouldn't be private enterprises or markets. They would be social enterprises and participatory planning!
Some might suggest some form of Pigouvian tax and while this would be an improvement on the present, and a good stepping stone forward, it still doesn't come close enough to deriving true costs or give those affected a process in which to participate.
This is why the environmental movement is fundamentally revolutionary. In order to sustain our environment in a responsible way we need to have a system in place that includes the true costs of doing business. To do this will require both producers and consumers have an incentive to reveal those costs. This will in turn require a revolutionary approach to allocation which will also require a revolutionary approach to property rights, among other things (i.e. remuneration, division of labor, social participation).
We don't have that system yet but it is within our grasp. Now is the time to discuss these issues. Environmental groups are doing an excellent job of changing our consciousnesses. Once a week garbage collectors collect recycling bins and my street is lined with those bins; and "green" products are becoming so increasingly popular that many Kroger's have entire isles reserved for these products. True, some of these products may not be as green as they are advertised but that's not the point. The point is that the buyer is not only conscious of their consumption but willing to pay more if they feel they are doing their part.
However, some questions remain. Why are we not sustaining our environment? What institutional boundaries are playing a part in this - Is market behavior encouraging us to race for the bottom of the barrel? How can we alter those boundaries so as to sustain our environment? What can we do to begin altering those boundaries? What are we waiting for?