I think the sort of person who likes it values the "test of time" aspect of it and trust that vim will still be there in the next three decades, just as it was there for the last three. It's super easy to install, and is indeed preinstalled on almost every Linux installation. So people can learn its ins and outs and do extremely fine-grained customization to their desire. People who get annoyed by tiny details and don't want to put up with it. The downside is that you need to carry around your config files and if you sit at a colleague's computer you don't get the same standard experience. And the fragmentation.
There's of course also the "hacker street cred" aspect of it, to feel like a real serious developer. Or simply being fed up with churn and saying "I'm too old for this shit". JetBrains IDEs might change next year due to some new design fad. Or they may go bankrupt.
In my opinion, valuing boring old tech is good, but you shouldn't make a crusade of it. I choose to put up with some churn and inevitable tool changes for practicality. Yeah, some things have to be relearned this way, some changes seem pointless, but the overall effort may be less if you just learn to be flexible and say "ok if JetBrains goes bankrupt, I'll just learn the next popular IDE like everyone else and be done with it" instead of prepping in my bunker with my vim config files.