Here's why I see gaming different. Only a handful of games, dominate the majority of the user base.
While it may seem that way on the surface, there's no chance to ever play your old games again.
Some games are replayed a LOT, especially single player, there is still TONS of people still playing Fallout 4 and New Vegas, Mass Effect, GTA San Andreas, and more. That also doesn't fix the other software issues like CAD, just throwing a few top games on this is not going to win over the market. Apple has had top tier games in the past and it was a mere blip.
You need at least several major game studios onboard and committed and that means Apple would need to pump CONSIDERABLE dollars to make this work, not just on their side side.
Nvidia, AMD, Intel, Dolby, and Microsoft all throw money and assistance at developers to make games run better. Could they? Yes, but they will be starting almost from ground zero. Yes, they can pull from Linux, it will help, but MacOS X was built on BSD and has migrated almost entirely away from it. Much of it still works, but it doesn't mean it's a straight shot, especially when you start getting into drivers and hardware. And it still offers no incentive to the game studios to bother.
Another thing Apple will absolutely have to do is change how they handle system changes and drivers.
There's talk on Slashdot right now about this, someone mentioned it and some blew it off as never having seen an update cause issues. There's a reason some printer drivers have one for MacOs 10.4, 10.5, 10.6, etc... Because they don't all work. Firewalls are also a massive pain in the neck on Mac, Little Snitch in particular can usually can only handle one or two versions before being shut out by Apple's changes. There's also Karabiner which was essential to many to remap keys, again, shut out by security changes on Mac (Karabiner Elements is, or at least was not the same and took years to get there). It was even worse on Nvidia gpus, on those it wasn't even major updates, even minor updates were breaking the drivers. granted, some of this was due to it not being Apple approved... Seriously, wtf. "But they don't need drivers..." Anti-cheat. Any update can break the anti-cheat systems. Can you imagine 2077 getting locked out on day 2 of release and Apple taking 4 months to fix it?
This is something people also do not get about Mac.
It's a VERY, VERY closed ecosystem and they steer it exactly how THEY please, you already know this, but it;s so much worse than people realize. "Oh, we locked you out with an update, oh well". "Oh we forgot to approve your app for our store, oh well., sorry *shrug* They had reviewed the Floatplane app MONTHS earlier, they just never bothered to approve it and let it on the store. When Nvidia leaked they were going to be the new GPU, Apple immediately cut them and reworked the systems to cut Nvidia out and don't forget the Iphone 4 debacle where they had the nerve to tell customers they were "holding it wrong". Everything is Apple's way or the highway, and they aren't always in any hurry to help anyone but themselves. This sort of attitude isn't going to go over well with game studios when they drop a billion dollar game like 2077. "Oh sorry we did review your app and it's approved we just left you on a shelf for 4 months missing your release window" Or worse still, they denied it for some weird reason. Imagine pouring all that money to put the new BF or COD on Mac and then gets denied listing or gets stuck on a shelf. When you have people willing to pay $5k to $8k for a GPU, do you think those people will be happy if your game is delayed due to Apple just not giving a darn? This may be why some cad programs are not found on Mac.
Now, you can say this won't really hurt the bottom line, it may not, at least at first. A push into the arena would bring increased sales even, but as these issues pile up, do you think those people will come back for another Mac after? Absolutely not and it will be another generation before they can attempt to recover that ground again. It has happened before, it can happen again.
By the way,
They had a lock on the software side before, and while they did change cpus, they were still at the mercy of whoever made their chips and those companies ensured some stability and compatibity from codecs and firmware down to the socket itself, that's no longer the case. They control the entire machine from one end to the other all the way down to the silicone and pcb (scary thought considering the T2 and other issues). If they decide to purge some hardware enhanced codec for size or something and your program relied on it, too bad. Just look at Iphones and Ipads, especially older ones if you want to see where this is heading. they keep saying they won't lockdown the software, they don't really have to when they can lock down the hardware to this extent. "You got your 4 years of updates, buy a new machine. it still works? Not anymore!"