Apple is one of the worst companies to deal with when it comes to development. They have only themselves to blame. Their tools for the M-Series Macs do make porting easier (Metal is nearly identical to DirectX 12 and mostly needs just a wrapper to remap functions from the latter), but the biggest problem is support.
You see, unlike Microsoft with Windows, which only ends support for an OS every few years, Apple abandons their OSes on a yearly basis. That means having to constantly shift the goalposts for which hardware is compatible. This is the problem World of Warcraft deals with every expansion. Because of how Apple designed XCode, once Blizzard moves to newer versions of XCode, older OSes get cut off. It wouldn’t really be much of an issue if the OS cadence was every few years, but yearly abandonment forces shifts that screw players constantly. I had to move to Windows instead of macOS, which is my preferred OS for this very reason.
The end result of all of this is that Blizzard no longer wants to develop and support a platform that constantly shifts the goalposts, porting tools or no porting tools. And make no mistake, Apple’s IGPs are still the Achilles’ Heel, even on their M-Series Mac Pro because eGPUs are no longer supported and in the case of the Mac Pro, no graphics cards at all are allowed - they’re blocked at the firmware level. Blizzard doesn’t want to deal with this anymore and now only maintains the previously available games on macOS at a bare minimum. You can see this with Diablo 3’s current issue of a missing dictionary key in the info.plist file inside the Diablo 3 app bundle. It’s the easiest possible fix and Blizzard hasn’t fixed it for months. The only reason WoW gets better treatment is because it’s a continual cash flow, something the Diablo games are not at large (even D4).
I don’t like it anymore than you do, but it is what it is. My 4090 would smoke the everloving crap out of Apple’s IGP. WoW only gets a nice boost on M-Series Macs because the ARM64 CPUs are in fact beast mode and WoW is entirely CPU bound. But you still have to sacrifice quality to get playable framerates due to the weaksauce IGPs and lack of third party GPU options. I’d have scrimped and saved for a Mac Pro if Apple allowed actual good GPUs to be used in conjunction with their CPUs, but they don’t.
Apple played its politics and angered a longtime developer that originally started out with macOS ports alongside their PC versions.
Fun fact: I could upgrade to Sequoia right now on my hackintosh…if I wanted to use just the IGP on my CPU. Apple refuses to sign nVidia’s drivers so my 4090 can’t be used for anything but an unaccelerated 2D raster with no resolution options and D4 does not run on IGPs.