The potential user base for skyrim on macOS is much lower because there simply isn't a large user base of gamers on Mac platforms. Mac users of Steam represent 2.45% of the total user base in the following survey: https://store.steampowered.com/hwsurvey/Steam-Hardware-Softw...
That's a circular argument. No content or support is the reason there are very few Mac gamers. There are an awful lot of people out there who have a Mac and play games on other platforms and devices. Probably even people who bought a pc just to be able to play games on it.
It is not. Many developers have tried and stats have shown the cost of porting Games to Mac, as well as maintaining it with each macOS changes were not sustainable with its revenue generation. That is at least for Games coming from console or PC.
This may change if those Games come from Mobile Platform.