Just tried Steam for Mac the other day, and there is a very good reason why it's so low. Modern macs don't even let you play games made for Mac!! Since 32-bit support was dropped, you pretty much can't play any Source games like HL2 or Gmod.
Yeah, most of my games don't work on macOS (I think ~1/4 do?), and most of my games do work on Linux (>3/4). So I don't use my Mac (work computer, my boss is cool with it) for gaming and instead use Linux.
Oh I know. I have a linux laptop that I use for gaming. I'm just going to a party where we plan to play gmod and some of the others don't have laptops so I thought I'd see if my Mac would be suitable. It wasn't.