why not just skip the middleman
Because many people take for granted their advanced understanding of Unix systems that allows them to get into the "meat".
If you're the type of person that is excited by a terminal display and prepared to read a whole pile of documentation, then sure--go straight to Arch, or Alpine if you're insane. But most people want something that's familiar, easy to set up, and will never force you to open a terminal. That's Mint (plus a number of other beginner-friendly distros). And most average people are perfectly happy to stay there. And that's perfectly fine.