> Tailwind allows them to add a few classnames and the page looks great
How is this the case any more than "raw CSS allows them to add a few styles and the page looks great"? You can't just haphazardly throw styles onto the page and it'll magically look good cause it was made in Tailwind. You design the exact same way you would if you were writing raw CSS, it's just you're putting the styles in the HTML class tags instead of modifying the CSS directly.
A person who's bad at CSS is not gonna be any better with Tailwind.
What it does is ensuring Locality of Behaviour, and css properties not leaking in other component of a web application.
It's essentially the same as css scoped to a single component.
If you copy the examples in the Tailwind docs it looks like your ripped off Stripe. If you copy the examples in the MDN css docs it looks like you ripped off a decade old govt site.
For example, building your own type system or JS framework would require a lot more code and man-hours than using margin: 4px vs m-2.
With Tailwind, whatever the actual merits, the biggest points of traction (IMHO) are the frankly excellent example sites[1]. You can click through numerous examples, all load quickly and without ads, that give you numerous variations of components, layouts, and even full pages. You can spin up a vanilla HTML or React app and ship good looking pages very quickly, esp. if you are bad at design.
[1]: https://truerev.com