Green Energy

In Europe I think it's mostly because of fear and fearmongering, for example by conservative groups such as greenpeace. (1)

They argue from an emotive point of view: nuclear energy feels unnatural, scary, industrial. Gas power generation on the other hand is the same old familiar technology, the enemy we know, with externalities we all seem to accept already (despite them being known to be worse for all).

For example, considering climate protection as the only goal nuclear power is a viable option for some. Most others however consider nuclear phase-out as a major Energiewende-goal. (Also from (1) )

Modern day lysenkoism, in essence.