Comment by tracker1

Web rendering has a rich ecosystem of tooling around a vast level of support for styling, layout, localization and accessibility support. By extension, it's one of the largest baselines in terms of knowledge, support and talent with at least some experience with.

This, of course, comes at a cost of performance as CSS alone is very complicated and has a lot there to support. On the flip side, there are many things that are easy to do with HTML+CSS that are much more difficult with native UI frameworks. Just the reflow support for multiple sizes/scaling in browsers is hard to match.