Yeah, the reason why people deride it, is because it's practically equivalent to:

div style="flex: 1; gap: 2em; margin-top: 3em; margin-bottom: 3em; ..."

I had to look up what these do, so they might not be precisely correct translations, but hopefully, you get the idea. It's mostly like using inline styles, and like not using classes.

In some scenarios, these frameworks might simplify certain things, like how my applies two CSS rules. And they reduce the visual clutter of inline styling somewhat.

But overall, it feels like people are dissatisfied with semantic classes, but don't want to lead the discussion for using inline styles, so they grab these CSS frameworks to pretend that they're not using inline styles.

It is fundamentally a difficult discussion to lead, because inline styles feel great, while you're writing them. They're less great for maintenance.
But semantic classes definitely have long-term problems, too.