When I worked Tech Support at my college as a student worker, Macs were really big in the Psychology and maybe Biology departments about 2 decades ago. They seemed decently popular with students, and I think even more so now.
They are also really big in the graphics design industry. So I could see his 30% percent of desktop/laptop being correct.
I do think your Steam Hardware Survey is a much more relevant number though, since it focuses on actual gamer users.
This has been brought up a lot of times on the forum, here’s a few threads which had really good insight/discussion, from what I remember when I read them at the time:
Bottom line is Acti-Blizzard has the ability to do a much more in depth ROI study than all of us “outsiders” on this forum. They can estimate how much it would cost to do the development, deal with the road blocks Apple has put in place, and can estimate their potential profits. They are a business with the goal of earning money. So the fact that they have stopped Mac support for legacy D2, and never included it in D2R, to me, says they have done the math and decided it doesn’t make sense.