Anyone who realizes how bad things really are will also realize how small a single act of sabotage would be on a global scale. Anything an individual is capable of doing would be relatively minor and then their life would be over, and any group of people who could maybe hit hard enough to matter just gets targeted by government counterterror organizations.

The charges for blowing up infrastructure are pretty hefty, especially if it’s politically motivated violence.

Also a lot of fossil fuel infrastructure is stuff like pipe lines and refineries, and popping a pipeline will do a shit done of damage to an environment.

There’s a group called Deep Green Resistance which does advocate for exactly this. In fact, they want to destroy industrial civilisation altogether, which possibly explains why their movement hasn’t really caught on.

Aside from them, Ted Kaczynski, better known as the Unabomber, thought similarly.