So there’s a couple factors to consider why Blizzard and other gaming studios have stopped trying to make their games compatible with Mac.
#1 reason is the amount of Mac users versus PC. Which just comes down to time spent to tweak the game to be compatible with Mac and if it would even be worth it. Blizzard has the numbers, and given their most recent decisions to not support Mac it’s obvious the majority of their players are on PC.
#2 reason is Macs use Metal, which is Apples graphics API, instead of using DirectX, which the majority of PC games run off of. Essentially it comes down to tweaking the game to become compatible, but again, referring to reason #1, it’s probably not worth the cost.
Now I agree it sucks for our Mac brethren, in a perfect world you could play every game on every O/S or platform you wanted. Sadly we do not live in such a world, and realistically speaking, I don’t see this changing for Mac users.