Users do not care about that. They care about when things they paid for stop working.
But that's not what drives the market for Mac gaming. What matters is what kind of return on investment developers expect to get out of porting to macOS. They don't particularly care whether the port keeps working for four years or forty, because they'll make basically all the revenue in the first several months.
Now, if users become reluctant to buy Mac games for fear that they'll stop working unacceptably soon, that could have a meaningful impact on demand for Mac games. But even if Apple made it official policy that they would break games after four or five years, that wouldn't completely kill the market for Mac games. If Apple made it cost-prohibitive to get a game ported to their platform in the first place, that would pretty much be "game-over for gaming on macOS".
If you can't play your old games it makes the entire platform unattractive to players, which in turns makes it unattractive to game developers.
But tbh Mac was hardly a gaming platform to begin with.
>it makes the entire platform unattractive to players
The platform has never been "attractive to players" to begin with.
Now we have Arcade though and easy porting to iOS though, which could open a multi-billion market...
They certainly weren't making much money off these particular games even before Apple announced the deadline for going 64-bit. It's unfortunate and disappointing for customers who had already bought those games, but this deprecation didn't shut Aspyr out of much in the way of future sales.