> Why are people not using the system python? Perhaps it's too old or not old enough for some library that they have to use.
If you're on a "stable" distro like Debian or Ubuntu LTS, that can be somewhere around 5 years old at the end of the stability period. And your system probably depends on its Python, so if you need a newer version of a library than the system's package manager provides you can't update it without risking breaking the system. Python itself has added several very nice new features in the last few versions, so anyone stuck on Ubuntu 22.04 LTS with Python 3.10 can't use newer Python features or libraries through their system's package manager.
I get it, but one can "just use Artix" or Arch or one of the other rolling distros where everything is always new. The only reason for being wedded to Ubuntu IS long term compatibility and that feeling that Ubuntu will fix security bugs but otherwise keep things "old".