I'm not sure what @LtWorf means, exactly, but one reason I can think of is that on Linux (Gentoo & Debian at least), the system package managers are not putting pip in place by default with python itself, the way they used to. The rationale, I believe, is to steer users towards using the system package manager or only doing ~/.local style things.

EDIT: So, you get threads like this https://stackoverflow.com/questions/65651040/what-is-the-rec... and so on