There are some niceties about some native UI frameworks... that said, they still tend to have shortcomings. Often don't work or have a really poor experience for cross platform dev or deployments. It also doesn't necessarily cover accessibility integration, which I've experienced the most pain in dealing with (at least going back into the 90's, far less experience recently).
Yes, out-of-the box cross-platform is the main thing going for HTML+CSS. It's an undeniable fact.
As long as you don't do anything fancy on the page, accessibility is now great for HTML, too.
However, since it lacks everything that makes a UI useful [1], all the custom components everyone is busy re-making from scratch make the web a miserable place from accessibility point of view [2]. Much worse than native frameworks which often enjoy deep integration with the underlying OS's accessibility features.
[1] See the work by https://open-ui.org and the many, many, many UI components most UI toolkits take for granted and have out of the box
