I get that on Steam, MacOs was more popular than Linux due to the sheer size of its user base, but how on earth do you play games on a Mac? I got my first MacBook from work AND because it was a work laptop not intended for gaming, but that didn't stop me from installing steam and try... Like a 10% of my Steam library? What?!?! Yeah, I can play Team Fortress 2 and Stardew Valley, maybe some RetroArch for slow working days, but not much else! How was MacOs the second biggest platform on Steam with such a small compatibility list?!
It's because Apple keeps shooting itself in the foot gaming wise. Instead of embracing open standards they made Metal. Instead of keeping Open GL up to date they let it languish for ages until finally Metal came out. Then the transition to Apple Silicon and dropping all 32 bit support killed a ton of old apps.
About 10 years ago Mac gaming was far better than it is today. Pretty much every game that ran on Linux ran on Mac.
Linux took Macs spot less because it's gotten so much better, and more because Apple has shot itself in the foot. Without the steam deck Linux would have overtaken them eventually but mostly because they're bleeding gaming market share.
For me (15-ish years ago), it was because I only had 1 laptop to take notes on in college, and it happened to be a Macbook. My gaming was limited to blizzard games and anything that just happened to run on Mac in steam, like valve games.
I bet most Mac gamers are in the same boat. They didn't buy it specifically to game, but they'll still play what they can.
Apple's macOS has been the second most popular operating system on the Steam game distribution platform for a long time, but that has now changed.
Linux has surpassed macOS for the number two spot, according to Steam's July user hardware survey.
Steam regularly asks its users to give an anonymized look at their hardware, and the company makes the information it gathers available each month.
The Steam Deck was first released a while ago, but it only became widely available without a waiting list last October.
It worked with game publishers to see high-profile releases like Resident Evil Village and No Man's Sky in recent months, and those games run pretty well on modern Macs—certainly better than similar titles on Intel-based Macs with integrated graphics chips.
It also announced a new gaming porting tool in an upcoming version of macOS that works in some ways like Proton, as seen on the Steam Deck.
Developers go where the money is, and that is Windows. To support Linux, they don't need to do anything. To support Steam Deck, they usually don't need to do anything, except maybe adjust text size based on screen resolution. That's it. To support macOS, they need to support a completely different rendering pipeline, ensure all of their dependencies support 64-bit, and now potentially target ARM (Rosetta, the x86 -> ARM layer can have a big performance penalty). Also, Macs don't have very powerful GPUs, so even if they do support macOS, the bigger titles will probably run poorly anyway.
So what are they going to do, put a ton of dev resources to properly support macOS, or put one guy for a couple weeks to support Steam Deck/Linux?
It has absolutely nothing to do with cost of hardware and everything to do with cost of supporting the platform vs number of potential customers.
A couple months ago Apple released some code for porting games that supposedly handles having to write custom code specifically for Metal. It's based on Wine so it seems similar to Proton, but Apple probably wants developers to package their games and get them approved for sale on the app store or whatever instead of having users just running their own games. It looked hastily put together when I checked it out, but I don't develop for Macs anymore so I haven't actually used it. It's too soon to tell if game companies care to port their games and go through retesting that the graphics work using the API translation layers to run on different drivers and hardware.