Yeah, selecting a stack IMO has more to do with scoping your goals.
For example, if you are an indie dev who will be developing a project solo, pick whatever you're best at, because all that matters is the product.
If you're an open source project, that's a different story. If you're looking to hire engineers, also a different game. And if you're the creator of Ruby on Rails and have created a giant personal brand around being contrarian and ignoring the new-hotness in web dev, then your choice is made for you.
I'd also say that a lot of people expecting to eventually hire on developers don't have to pick the tech stack that will scale to a 30 developer team. I've known a lot of very successful companies where the core tech was rebuilt/replaced as the team demands grow. And a lot of them probably wouldn't have gotten there that quickly if they make decisions around a 30 person team when they were 2 people.
Not only is it mature, but it's his framework. Sure he's not the only maintainer but he's the original author. It makes sense to use your own tools; specially if they're successful.
For example, if you are an indie dev who will be developing a project solo, pick whatever you're best at, because all that matters is the product.
If you're an open source project, that's a different story. If you're looking to hire engineers, also a different game. And if you're the creator of Ruby on Rails and have created a giant personal brand around being contrarian and ignoring the new-hotness in web dev, then your choice is made for you.