I guess it depends on how they are using Macs to assist in game development. Most big titles are going to have lots of storyboards and conceptual art, and there are also music scores to produce. It’s possible the “artistic” part of these games are made at least in part on Macs, while the actual development is done on Windows machines or console development kits.
If it’s a PC game, it’s likely to be targeting DX12, and I believe MS makes it relatively easy to license and develop with DirectX. Macs can’t use DirectX, so the games must be ported to OpenGL/Vulkan. Some studios do this, but many do not. Many Studios contract out the porting to Mac. I guess not enough Mac owners are gamers, or those that are just use Bootcamp, to make porting titles cost-effective.