React is very much the dominant framework,

Unless you include libraries, in which case it's jQuery. There's still far, far more sites using jQuery compared to React. jQuery is trending down a bit, but the majority of the top million sites still use it.

Not everything is a web app... A large number of sites are mostly static content with small amounts of interactivity. In those cases, React (or Preact or Vue or whatever) are generally overkill. Those types of sites are migrating away from jQuery, but they're migrating to either lightweight libraries like htmx, or just vanilla JS.

I wonder if an AI coding tool would even suggest Preact as an alternative to React? 🤔

I don't use any AI coding tools for personal projects, but at work we use custom tooling built on top of Claude. I'll have to check if it suggests Preact once I'm back at work.