Especially because the last step is less "make it" and more like "npm add it".

The browser has "ready-made components". React (et al) also has "ready-made components". React's selection is a thousand times larger. React also allows you to make your own. The browser doesn't [1].

Who can blame developers for skipping the inconvenient half-solution and going straight to the all-encompassing ecosystem

[1]: It does, but web components are too unwieldy to compete with React

The vast majority of the patterns in the ARIA APG require bespoke JS plumbing for proper focus management, keyboard controls, and etc.

Isn’t datalist doing that? Last time I had to build a combo search box I was pleasantly surprised to learn about it