There's that, and the fact that web component technology is really a set of convenient primitives that don't do anything better than libraries and frameworks, besides the fact that they come built in to the browser. Then of course there was the rash of bloggers who were huffing and puffing over how inferior web components are, despite how their existence and even the ability to define custom elements alone are a pretty good idea. From what I've read over the years, I think that there's been a lot of bad press early on, and perhaps there were some very misguided individuals who think that web components "fail" because they don't live up to React. The point was never to replace React. A lot of people are still complaining about the polyfills, even though the only thing it says about web components is that they will eventually have full support and not need polyfills. Above all, all the polyfills combined aren't even half the size of a lot of app builds in the wild.

To expect web components to "catch on" in the same way that React and Vue have is a bit dumb, but I would like to see them adopted in a way where there's a good story around their use in frameworks, rather than a replacement.