Well it made sense for France for multiple reasons even in 70s. France didn't trust / like Anglophone dominance in the world. They brutally kept their colonies, sometimes to the bitter end. The mistrust to US/UK hegemony and the strong sense of nationalism is the reason we have Ariane and Airbus programs. Henceforth, they also invested in their own nuclear program. To make small and cheaper nuclear weapons, you need plutonium which can only be created in reactors. Even with that knowledge they burned fossil fuels majorly before 70s.

France built majority of their nuclear reactors after 70s oil crisis. So it made sense to have independent resources for them. So they won't need to rely on other nations, some of which were their former colonies that hated them. They had two strong reasons to keep a nuclear base electricity generations.