We can rant about the definition of an PC. Yes it’s all the same hardware. So if you take PC as in Personal Computer, yes an Mac can be described as an Personal Computer. Although when marketing started on Mac they had the slogan “you’re not buying a PC you are buying a MAC!” so they distance themselves from the PC market.
The most common Personal Computer runs on Windows (see image below). Like i said earlier it’s has to do with the OS and how it works. Windows and IOS have different API’s how to manage stuff. Mac’s haven’t really been an gaming platform. Porting game to the other OS takes time (read Money).Because the majority of the consumers are on windows PC’s that’s where the money is made.
When Borderlands 2 did well it got an MAC & Linux version, so maybe you just have to wait a bit longer (or buy an Windows PC). But the chances of a MAC version is higher than Battleborn coming to WiiU.