You have to remember the biggest appeal of tailwind is that it throws away the entire cascade of css. The people that reach for it are choosing it because it offers less functionality, and is therefore simpler to reason about. I hesitate to say they don't understand css, I'm sure some of them do, but in my experience the devs that reach for it are the same who deride css and make statements such as "I have better things to do than learn css"

I think there's plenty of developers that are perfectly competent with CSS who still reach for Tailwind.

You're right that Tailwind throws away the cascade, or at least enables developers not to have to think about it (under the hood, Tailwind 4 uses pretty modern cascading features like layers), but people aren't reaching it because of a lack of understanding, they're reaching for it because as front-ends get increasingly componentized, the cascade becomes less and less of a benefit and more of an obstacle to be worked around, and something that gets that obstacle out of the way becomes more attractive.

Don't forget that, in my opinion very positive way, it also normalized the concept of "uniform measurements". Every instance of `rounded-md` is the same on a site.