Market growth potential aside, a small portion of users doesn't necessarily equate to abandonment="sensible economical decision." If that small portion is more profitable than the majority, then it's worth serving. That's pretty much how Apple got to be where it is today.
They didn't, they developed for DOS well into the Windows 95 and 98 era, at which point Windows had captured the PC market.
Indeed, but that's not the case with macOS and Linux players.
But... it's not. Not even close. It's tiny and Linux costs far more to support due to variations in configuration and flaky APIs.
The difference being that Microsoft went all out in building subsystems (WinG and later the various DirectX technologies) for gaming and courting game developers to target it while Windows 9x was still new and popular.
Nothing similar has occurred for any of the Linux distributions nor is that likely to occur.