We are not "back" to windmills that give 3 MegaWatts of power because they never existed in the first place, like affordable solar panels with 20-40% efficiency.

Progress is not automatic. It is millions of times harder to create or improve a technology than imagine it. And also takes lots of money.

We have nuclear tech because Manhattan project, because WWII(and because they were scientists coming from Europe that were scare of Hitler). It took a tremendous amount of money and sacrifice to get there.

With the caveat: for commercial travel. And even then it’s partly due to noise restrictions. It’s not like the technology for supersonic flight isn’t widespread.