Maybe the difference is that other people build apps with lots of components. When I write HTML I mostly build web pages - a lot of text, some images, and maybe a menu.
I need to be able to tweak properties among a lot of different elements at the same time. E.g. change the font face on all elements in the main area, change the color of all links that are not special links, rotate all titles and underline them, and so on. It's an iterative approach, as I evolve the design in HTML (I don't have a designer team that hands me a psd I just have to copy). To do this with Tailwind, you'd have to use components, and you'd have to add another layer of abstraction to affect the right components together.
And I know nobody really uses CSS Zen Garden style themes - but it is great to be able to take a HTML snippet and use it in another project with minimal changes and a different CSS design.
CSS has shortcomings - it's missing a way to "include", it could have more complex selectors, it can get unwieldy in larger projects - but it is also does a couple of things really well.