My hot take, pretending I was an environmentalist, is that fossil fuel/climate change is the object d'ire for environmentalists only because nuclear ended up not gaining traction. The masses of environmentalists have moved on to a different front of the battlefield for protecting the earth but would return if nuclear gained traction.

It's kind of like now that humans conquered polio and smallpox, the next challenge toward advancing the human race is ridding ourselves of cancer. If polio and smallpox returned, we'd be back to fighting those.