I think if Rails had focused on giving real first party support to interoperability with whatever frontend framework you brought to the table it would be so much bigger right now. They put a lot of work into Hotwire but I just want to use React, and I'm sure others want to use what they're familiar with.
I’m hardly an expert with Rails, and I integrated React twice, on two very different sites, using API controllers. The nice thing about React is that you can limit it to an island on the page, and don’t need to buy into the router, etc. that said, I did disable Hotwire to make my life easier.
Rails can be API only and use any frontend you want.
Hotwire is the default and they develop it because DHH wants to, but they're not putting up any barriers to you using whatever you want.
Also, DHH doesn't seem to care about how big it is. His stated goal is for it to forever be a framework that's usable by a single dev.
API only Rails has been a thing for a long time: https://guides.rubyonrails.org/api_app.html
Many teams use this with React.