E.g. for Germany - the most high profile nuclear exits: - nuclear and fossile energy producers were the exact same companies - why would they fund activists to campaign against their own assets? - coal mining and plant employees were (around the first exit) part of a significant worker voter population, especially for the social democrats but to a lesser degree for the conservatives, too. The largest state was heavily dependent on the coal industry and SPD/CDU politicians regularly moved to/from leadership positions in coal-dependent energy producers. No party except possibly the Greens would have remotely touched a coal exit and discussions around that only seriously started after the second (conservative reversal reversal) nuclear exit. - gas and nuclear fuel in major quantities came from Russia, from different Russian state companies - why would they cut into each other's business by funding activists? They were happy for Germany to depend on them in any and all ways. - the second nuclear exit was a political play for voter sentiment by conservatives after Fukushima - they didn't even try to explain why nuclear should be kept for all the reasons they reversed the previous exit and still killed of the nascent booming solar/wind industry - they certainly were not renewables activists. Just recently the reverse happened as part of conservatives pre-election promises to rebuild nuclear as a play for voter sentiment due to temporarily high (war-dependent, already normalized) energy prices. It wasn't important enough for them to include in the government coalition plans in any way whatsoever - the main conservative agitator for nuclear has now had to agree that nuclear is economically dead.

The reality is that nuclear in Germany was already dead when the first exit was voted on - nobody had built plants in a long time, nobody had any plans to build them. If not for the exit plans to start a renewables transition, fossil usage would be far higher today and because of the exit reversal and delay in coal exit due to the conservatives it is much higher today than it needed to be and we're much more dependent on Chinese manufacturers, too.

At most activists were somewhat involved in voter sentiment at some points, but it wasn't particularly crucial versus the actual economic and political realities.

The reason is, I think, that the progressives have rationally better policies - ones that become mainstream decades later, including much of what is mainstream now - so by demonizing the progressives the center and right prevent people from actually considering the policies.