But honest question, wouldn't those years of wrestling with the right UI framework be better spent learning the underlying CSS rules and adopting a simple pre-processor that gives you programmatic generation for repetitive bits?

Because in the end, tailwind is better than bootstrap, but it's still the wrong way and incentivises wrong patterns.

And by making it "standard" it makes everybody new to the field start with it and use it, foregoing learning the CSS. And will be supplanted at some point, and then there'll be the dance again. And again. It's just this that I don't understand.

At the point you're customising tailwind and classes you run into the same problems as with CSS without clear guidelines/organisation. So the only way to not run into that it's to use it as inline styles but with classes...