Providing ready-made UI components and templates has never been a million-dollar business, nor should it be.

Arguably many websites and apps desperately need a good component library because it's very clear the UI sucks without one. Lots of people spending a few thousand dollars on their UX is not unreasonable at all, so the best-in-class library (whether that's Tailwind is a separate point) should be able to make a lot of money.

You could easily level the same argument at any library: "This thing is simple so it shouldn't be worth millions." That's just the wrong way to look at how selling works. If you make something that solves a lot of people's pain point (Tailwind) you're going to make a lot of money until someone else sells something that makes it even easier (AI). That is a tale as old as time, and the fundamental basis of how startups disrupt incumbents in an industry.