Because they don't want to help the environment, they want to feel recreationally outraged and like heroic revolutionaries ending evil. Environmentalism is just

Because they don't want to help the environment, they want to feel recreationally outraged and like heroic revolutionaries ending evil. Environmentalism is just their latest wedge to insist that the solution to all problems in the world is their preferred revolution. They actively dislike and frustrate measures that would actually help address real problems, as it would take away their excuse, and they'd rather the problem continue (or hopefully get worse) than admit that they're not the solution. That last bit is often quite explicit - "We can't end $x until we end capitalism!" etc., and accusing more moderate groups of being bourgeois infiltrators or various -isms for daring to actually get something done instead of shouting about an ill-defined utopic revolution ad infinitum And they majorly slow progress and tarnish public opinion of legitimate movements by forcing their way in. It's group narcissism