Some languages have a obligation to support older versions, provide upgrade guides. They have old baggage in the forms of old systems or processes that they can’t just abandon.
Sometimes it’s easier to just start over from a clean slate. Experimenting and seeing how it works. If it fails well you haven’t inconvenienced millions of users.
It’s all about experimenting, trying to see what works, what it’s good with and what it’s not good with. A language like Java can’t just change to experiment things. Some people are also fixed to the style and methodology that Java provides.
Aside from that, hobby languages are just hobbyist stuff.