It is interesting to note that essentially all the civilian reactor designs are really minor respins on 1950's plutonium producers pretending to be power plants, the very short (~6 months), low burn up fuel cycle gives it away as that is how you optimise for weapons grade isotopically pure Pu.
I suspect that the only reason nuke plants were installed in the first place, was as a means of maintaining the military nuclear infrastructure -- manufacture and production, and the knowledge base of actively experienced workers and engineers.
As soon as the Cold War started to wind down, so did the construction of new nuke plants. Now that there is much less strategic emphasis on nukes (they've pretty well matured in their role, and the quantity continues to decline as far as I know), there's less need for experienced workers, and plants are even closing.
As for actual mechanisms, I don't have any explanation, no. Correlation is great, but it doesn't mean anything in and of itself! Military-industrial complex? Look for changes in the regulatory atmosphere over time, and who's responsible for those changes? Possible. Just a suspicion.
The colloquial explanation is public pressure and poor economics.
That's not terribly satisfying to me, because public opinion can be swayed (the educated generally approve of nuclear power). For the budget on these stupid things ($B's), they could handily win a freaking election* if they budgeted a modest fraction of that to education, advertising and campaigning. Do they just not have their heart in it? A mere million dollars is serious getting-people-involved money, and we're talking thousands of millions. These things can't happen without a lot of people getting involved. Wouldn't they protect their investment by involving some advertising people? (Maybe they do, but keep it mostly local, where it matters most? Idunno.)
*The budget of the RNC and DNC is around $1B each, at least in presidential election cycles.
As for economics, that's largely driven by the astronomically staggering amount of paperwork needed for the whole thing, top down, bottom up, every component, every weldor, accounted for, accredited and licensed. Such a massive design inevitably contains mistakes and omissions, and there is no process to handle that. When mistakes are found, it just snowballs out of control. Take the Vogtle reactors for example: stuck in contractor disputes for apparently additional
billions worth of costs and legal fees, if I've understood it correctly.
Conventional power plants aren't much less dangerous, and are built on a regular basis, without nearly as much quibbling, and much leaner budgets. Simply enough: to build nukes, apply the same regulations to them, adding only what is needed to control and protect the nuclear part of the system. They'll pop up overnight.
Maybe the designers, builders, and perhaps owners too, of conventional power plants, are the ones lobbying for restrictive nukes? No idea. Someone, something, somewhere, definitely has it against them, that much is clear.
Tim