There's more to a language than the syntax. The libraries, tools, and the ecosystem of developers, documentation, support, etc. are much more important. There are quite a few academic languages that are interesting to people that never really gain much traction because the people behind them just never commit to proper ecosystem building.

Switching languages is a big time commitment. Or at least it used to be. I find myself more open to that now that I can hit the ground running with AI coding tools in most languages. But still, it's a time investment to learn a language, its idioms, its way of doing things, all the tools, libraries, and frameworks, etc. It's not something you do an in afternoon. And certainly not mid project.

The languages that people gravitate to are the ones that look like they are safe, future proof bets. If you are going to spend all this energy learning one, you want to know it's a good investment. Successful languages have lots of users, decent tools, good libraries, etc. Or at least they look like there are serious people behind them. Many people make these bets early in their careers and then stick to them as well. I meet a fair share of people my age that are still sticking to Java. Because that's what they learned when they were in their twenties. I'm 51 now.

Rust is a good example of a language that's hard to learn but managed to get off the ground because of the solid people behind it. It wasn't just an academic exercise: Mozilla was trying to solve a real problem and they managed to get a nice community behind the language and it grew from there. This is not something that happens a lot. People create new languages all the time. But many stay very niche and the projects around them tend to go stale very quickly if they fail to attract a community of users.