Apple is a pile of cash that has a few developers on hire. Most of the developers who made the Mac really great left Apple years ago, and the Mac's been a third-class citizen at Apple for over half a decade. Some guy deciding not to pay for Mac OS, for whatever reason, isn't going to break the bank at Apple.

Apple could make nothing from the Mac and it'd still be more than worth it for them to continue maintaining it because of the benefits it brings to their mobile ecosystem.