As mentioned up in the thread, If it was just a switch enabled in the background, and caused instability with some games, you'd likely have a lot of people complaining "hey the game's broken" or "hey this game is crashing" and it taking awhile for the community to suss out what's going on exactly and an increase in support requests to Sony or other third parties. Even on the PC, overclocked CPUs and GPUs unknowingly resulting in system or application instability are problems there, for example, because people don't suspect their own hardware failing in that way, or failing to remember the unsupported config they've left on.
Sony has already accidentally broken some games in the past with subtle changes in their firmware, so their skittishness of going back to old games and allowing for a blanket upgrade in performance is 10,000% understandable. I was genuinely surprised when Msft, had its <10% boost in perf for the XB1S play out for games retroactively, and I can only assume this is in part because I think it was a GPU-only change, not CPU, and they also have way more resources to go back and test this sort of thing that Sony just doesn't have.