We would love to have the game on Mac and Game Maker supports it fine. I even have the required module! The problem is that it is such a hassle to set up Mac builds due to Apple's restrictions, especially since I don't have a recent Mac available. As you've noted it is a hobby project and I have very limited time to work on the game, so a Mac version is pretty low priority right now. Sorry!
Thanks for the comments and compliments - it's encouraging to hear that there's interest in the game. Hope you get a chance to try it out!