You keep saying easy, so its easy to build emulators now is it? Ones that run every game at expected levels of performance? and then keep updating said emulator.
Question, are you a developer? you must have vast knowledge of development (of the PS5) to say 'easily build an emulator' (I presume you are talking about PS1, PS2 and PS3) or its easy to make every PS4 game run at 120hz on the PS5 (and this one dude has support for, what, 12 titles? if Sony are to do it they'd have to support thousands)
I am not saying it is beyond Sony's resources, but those resources are better spent elsewhere, you know, making NEW games.