No mystery about that. Environmentalism is not interested in an alliance. It does not need or want the left.
The hostility to 'productivism' (which the greens rightly see in Marxism and social democracy alike), is a coded hostility to the productive, ie the working classes. The concerns of the environmentalists are anti- humanist. They deplore population growth (nasty oiks moving into the neighbourhood), working class mobility (too many cars!), working class consumption (fast food is cutting down the rain forest), foreigners (too many Chinese - with fridges!), unless they are in a state of degradation that is called 'authentic culture'; they embrace the kind of organic social order that could only mean death for the left; their theories of equilibrium between man and nature are only a reworking of equilibrium theories in economics, with a wholly apologetic intent - 'sustainable development' instead of real development for the third world. Like the bourgeois apologists of old, they seek to justify the limits that are artificially imposed upon working class consumption by capitalism, as if it were a natural limitation, that will necessarily lead to disaster.
-- Jim heartfield