Every wonder why Steam has so few Mac OSX users? Might it have something to do with how few major games are available at all on Mac OSX?

It doesn’t exactly take brilliant insight to see that this is a bit of a chicken-and-egg problem, and so them taking this justification to avoid porting (and I think you’re probably correct that this is their reasoning) creates quite a self-fulfilling prophecy.

Yeah, the cost of porting to a new platform needs to be lower than the money you think you will make out of it.

I think Factorio's code quality allows the developers to make the ports relatively cheap.

Big studios have so many developers that come and go and just work on legacy code that seems to make assumptions about the platform on every level. The cost becomes too high and not worth it.

It's because one is greedy, but because it's bloated.

If I remember correctly the studio behind Mini Metro gave up Linux on their new game because it was too time consuming to run the game and test it. Obviously if you lack tests and need to have manual testers all the time, new platforms won't help you. (I'm making assumptions from the blog posts I read, I might be wrong about the real reasons.)

Every Mac game I own on Steam I could have (and honestly should have) bought outside Steam. The Mac App Store, GOG, Itch, direct from the publisher. It might have been more expensive, but Steam is such a piss-poor Mac citizen I am not surprised barely anyone uses it on Mac. It's not a clear-case cut of where obviously every gamer plays on Macs.