I was born in the late 90s so by the time I got involved in technology, my introduction to Unix and Unix-flavored systems was limited to Linux and MacOS. However, I've read about the history of Unix at Bell Labs, the BSD systems derived from research Unix, and the eventual commercial releases of Unix System V from AT&T themselves. I also see that HP-UX, AIX, and Solaris are apparently still maintained and get releases, which suggests that they are still being used in production in some places.
I'm curious if anyone here currently works (or has very recently worked) somewhere where proprietary Unix is still used for production. If so, can you tell me what they're used for and why those deployments haven't been moved to an appropriate Linux distribution?
Not suggesting Linux is necessarily better for all use cases, just wondering what keeps these small number of entities clinging to closed-source Unix with presumably pricey license costs.