Just look at the Mac Pro, it used to be ATX based which means gamers would buy it to upgrade the video card to play more games.
Did any significant number of users actually do that though? I do remember in the Power Mac G5 era that NVIDIA would, occasionally, vaguely support Mac gaming by releasing high-end consumer-level graphics cards for the Mac, but I truthfully don't remember ever hearing a single user account of a user riding the expandable Mac Pro wave for high-end gaming.
Some of the video games need a better GPU than the stock that comes with Macs. The Mac Pro since it was based on ATX standards would take a PCIe NVidia/AMD/ATI video card that could be replaced.
Tell me about a modern Mac made today that can exchange the GPU for a faster one.
If the Macs can't exchange the video card for a better one, they are losing the gaming market. More Windows than Mac games, and Bootcamp can install Windows on an Intel Mac to run Windows games but if the GPU is too slow for the top of the line games, might as well buy a cheaper PC with expandable video cards instead.
I've found Linux Mint or Debian on a PC ATX gaming system runs faster than on an Intel Mac with OSX and video games.
Apple is losing their customer base by doing a classic blunder that Atari, Commodore, etc tried, they don't know the target market of users. Apple is losing the Mac gaming market, due to price losing the Educational market, due to not having a pressure sensitive pen the Artist and creative market, and while Apple has the developer, web designer, and programmer market with Macbook Pros for Startups as the Macbook can book OSX, Windows, and Linux with Bootcamp, they've forgotten of their other markets that left a void that others like Google, Amazon, Microsoft are filling.
Did any significant number of users actually do that though? I do remember in the Power Mac G5 era that NVIDIA would, occasionally, vaguely support Mac gaming by releasing high-end consumer-level graphics cards for the Mac, but I truthfully don't remember ever hearing a single user account of a user riding the expandable Mac Pro wave for high-end gaming.