- Microsoft: Gaming has been a first class citizen at Microsoft for a while and I'm not sure if we can say the same about Apple. They just put tons of money into it because they have this competitive advantage. It's not only the games they bought/publish (Minecraft, Age of Empires, Flight Simulator, etc), but the platform itself (Xbox, DirectX, etc). Windows 10 also has a "Gaming Mode" as part of the OS for performance improvement which some games might have it turned on automatically.

- Hardware: PC Gamers usually customize hardware to have pretty decent power (GPU, CPU, Memory, etc) for relatively cheap when compared to Mac. In PC market, there's hardware competition for literally every single part of the hardware. For games that require extra power, you would need a powerful machine and, while they do exist in newer generations of iMacs, it's just damn expensive. Which brings me to my next point: market.

- Market: Although Mac users grew significantly, I'd say it's still pretty small when compared to PC. If you are a game developer, especially an indie game dev, you may find how depressing it can be to publish a cross platform game. It's not super hard given the popularity of game engines such as Unity and UE4. But the issue, in my opinion, is if your game has multiplayer, for example, you're probably going to have a bad time dealing with platform differences. Aside from that, you're going to have to deal with other platform differences in a lot of different levels. At some point, you're going to ask the question: is it really worth the extra investment? You are going to delay publishing your game for probably little gain. Developing for the larger market first might make more sense. Not only for indie devs but for AAA games too.