Sometimes blanket supersampling can create unintended issues. Like, if a HUD scales with resolution, or on screen text being rendered at fixed pixel heights, stuff like that. It depends on how the supersampeling is applied, and how the game is composed. You can see these oddities in older PC games run at higher than expected resolution, or sometimes even modern games run at lower than expected resolutions. Or even just strange resolutions. My wife at a windows tablet that has a 1080p screen but an intel GPU. She tried to play Titan Quest on it (an older game that still gets patched often) and I set up a custom 540p resolution. There are HUD elements that just don't render on screen at that resolution. But they do at 480p, so it isn't just a problem of not enough pixels. There are even games on PC that get weird if virtual super resolution is enabled, even if the game isn't run at higher than native resolution.
I would imagine there would have to be a fair amount of testing to ensure supersampeling worked, and then it becomes an issue of paying for that to happen vs it being "good enough" for most people. And who knows, maybe the custome scaler chip has some secret AI powered laggless edge detect antialiasing built into it.
