With the source code DLC it should be possible to compile everything for a Mac regardless, even if it's a bit of work. If we make enough money from the game, we might reinvest it into a Mac. :)
The number of sales is, however, negligeable - Mac has just 1.38% Steam users
PirateSoftware told [1] that the Mac was 0.02% of their sales - one in 5000 sales (and thus he dropped Mac support)
Don't reinvest in Mac for sales before you do the math.
If you just want a Mac, get a Mac. If you don't want a Mac, don't bother
I would happily test my software on macOS and Safari, but I'm not paying for that privilege. So a lot of my stuff just doesn't work. But Windows, Edge (and previously IE) and Chrome and Linux are all easy to test on so I do even though personally I only use Linux and Firefox.