The Mac is a weird counter example here, the move to 64 bits resulted in many games with official Mac ports (e.g. most of Valve's: Half Life, Portal, etc) no longer being able to run on modern versions of OSX
- They've been very diligent in the past about keeping their games up to date.
- Valve owning Steam means their flagship games are a strong signal about macOS support on Steam.
- If they really wanted, they could; they certainly have the resources to do so should they want to+; which means, they don't want to, which is a signal in the other direction: they stopped caring about macOS.
+ HL1 has a FOSS engine that apparently supports it, and more: https://github.com/FWGS/xash3d-fwgs/blob/master/Documentatio...