Look at Flamanville in France: budget triple the "estimate", 15 years to construct. France has more nuclear energy per-capita than any other country on Earth, so it's not like they don't know how to "do" nuclear.
Those who decline to play by the rules we have ended up with, don't get the contract & go out of business, or don't get elected. It seems like an incentive problem. And a possibly unsolvable one, for huge mega-projects like this -- constructed over decades, dangerous & high-tech, and completely useless until 100% completed.
Wind energy seems much more healthy in this regard. You buy off-the-shelf units, from a factory. If you don't like the first 10 they install, you don't buy the other 90, and still get 10% the power. It's much closer to buying cars, or pencils, which our society is pretty good at optimizing. Every year we improve the process, and these steps add up.
You are correct that wind has a lot more flexibility in this area than nuclear. It is also much easier to scale a project up by just adding more turbines. In the case of older, smaller turbines they can be replaced with more modern turbines that yield more power (called re-powering).
In general wind power and solar have much better economies of scale too -- the more you build, the cheaper it gets. Nuclear doesn't tend to follow that pattern -- although there are attempts to create it via small modular reactors (SMRS). The jury is out if that will succeed or not (early signs are not great though).
From the 90s to the mid-2000s there was probably a window for development in this area. But the nuclear sector stagnated as a whole, and then fracking made natural gas cheap enough that people wouldn't consider it.
The jury is out on SMRs still. They're promising a lot, and the tech and engineering has improved. But plunging costs of renewables mean the window of opportunity for nuclear tech is probably mostly closed in the West. This article from a highly respected energy sector analysis group is worth a read: https://about.bnef.com/blog/scale-up-of-solar-and-wind-puts-...
India and China are the big markets for nuclear right now -- their energy demands continue to grow, and they're building reactors as part of an all-of-the-above model. France MIGHT be a potential buyer of SMRs (their reactor fleet is getting close to end-of-life), but their nuclear companies have put a lot of push behind the EPR design.