There are better "gaming" distros, but unless someone uses their PC exclusively for gaming, when it comes time to install other kinds of software for school or work or whatever, they're going to get thrown in the deep ends of Linux.
But guess what does have two decades of software and tutorials to set up just about everything in existence? Ubuntu, and by extension Mint.
Sure you can squeeze more out of your games with something like Bazzite, but the general platform that anything Linux-native targets is usually Ubuntu. Sure there's distrobox and stuff that's like telling the average gamer to go set up WSL. It's not hard per-se but the amount of things to learn increases very quickly.
Thus, even though Ubuntu is very average these days, it's still a safe bet for new users.