But logical. Face the fact that Mac OS doesn't have the marketshare of Windows, or any of the consoles. Furthermore, the actual marketshare itself consists mostly of Laptops - many of those running on an Integrated GPU. Thats not even including those running older systems.
On top of this is a less efficient and much more limited graphics stack, that because of the way Mac OS operates does not permit for driver level optimizations and enhancements as is standard practice on Windows.
As a result, the number of people that can run modern games at a satisfactory level are few in number. And of those that can, they'll generally be content running it in Windows anyway (and possible on Linux).
Basically you increase complexity and decrease performance by porting to Mac OS, and you reach extremely few additional users by doing it.
For indie games its not as big of a problem due to their typical simplicity. The resource requirements as such are typically very low, any inefficiencies can be simply be overpowered, and advanced capabilities are rarely if ever used. Do note that most Indie games make minimal - if any - use of the GPU to begin with - so the weak GPU capabilities of Macs don't become an issue.
In addition, the typically low sales numbers (relatively) of Indie games means that even a few thousand sales to Macs will make a significant improvement. And due to the relative absense of games on mac OS, its easier to become visible to begin with, which is typically the biggest Indie challange.