[jamesfinlayson]

All of their games were ported to Mac in 2013 or so but that support has been wound back in the last year or so with Intel Macs dying, 32-bit Mac support dying and presumably no interest from Apple in helping keep the Mac ports alive.

[stephen_g]

From the blog post accompanying the source release [1], it sounds like the classic Source engine is only being made fully 64-bit just now.

> We're also doing a big update to all our multiplayer back-catalogue Source engine titles (TF2, DoD:S, HL2:DM, CS:S, and HLDM:S), adding 64-bit binary support, a scalable HUD/UI, prediction fixes, and a lot of other improvements!

So it sounds more like Valve just hadn't done the work to make it possible to run on more modern macOS (that has long been 64-bit only) until now. Not much Apple could have done except maybe tried to directly pay them to do it earlier...

1. https://www.teamfortress.com/post.php?id=238809

[jamesfinlayson]

Yeah. If it's been ported to 64-bit now they've probably dealt with the x86 assembly as well.