Well, the thing is, things like the classics you can download via PS+ premium show that the systems are capable of playing the games. It's just a matter of reading the disc.
This is inaccurate, I'm sorry.
The PS4 and PS5 are not natively capable of playing games from previous generations of PlayStation (well the PS5 can play the majority of PS4 games, think there's like 5 that don't work or something), so it's not as simple as 'if they could read the discs, you could play your old PS2 games on your shiny new PS5'.
Sure, there are a number of PS1, PS2, and PSP games available for download if you have PS+ Premium (discounting the PS3 games here since those are only available via cloud streaming),
57 to be exact. But the thing is, none of these games are being played natively on your hardware, they're all being emulated.
And that's where the big catch is: emulation.
Like this might sound crazy considering the age of the hardware, but the PS2 is still regarded as one of the most difficult consoles to emulate because of its complex hardware that even developers making games
for the PS2 would sometimes struggle to work with.
Hell, there's literally 49 PlayStation 2 games that don't work or have issues when played on the slim PS2 models. Yeah games made
for the system that have problems when running on later versions of the same hardware, that should tell you about the PS2 and its hardware complexity.
Like the PCSX2 emulator exists for PCs and can run the vast majority of PS2 games (according to the compatibility list, 99.15% of all PS2 games are playable on the emulator). That probably seems like I've defeated my own point, if PS2 emulation is so difficult, why can this emulator run nearly all PS2 games? Well, it's emulating PS2 games
perfectly that's the difficult part. Pretty much every game you can emulate on PCSX2 can be
played but only a handful run perfectly without any graphical bugs or any other issues that may require you to use speed hacks, switching to software rendering mode, etc.
And that's all stuff that's acceptable when talking about an entirely free and open-source emulator, but that's not exactly acceptable when talking about an official emulator, y'know?
So instead, Sony has to basically do per-game tweaking for every PS2 game they'd want to put on the service (and that's not even including things like licensing for third-party games) and that costs time and money. (And the big elephant in the room is that Sony's PS1, PS2, and PSP emulators
ain't that good to begin with. Like, I obviously don't know how you feel about it, maybe it doesn't bother you - but it is objectively pretty poor for a variety of reasons, so it's doubtful Sony would ever spend the time and money on developing a 'perfect' PS2 emulator so you could play all your old PS2 games. I'm not even going to mention PS1 and PSP games considering that even
if Sony had absolutely flawless and perfect PS1 and PSP emulators, neither the PS4 or PS5 can read CDs and obviously they can't read UMDs - so you'd still be SOL on that front)
And please don't get me started on PS3 emulation, there's a reason Sony doesn't even offer PS3 games outside of their cloud streaming thing.
(Of course wanting people to keep spending money
is also part of it, so you are right on that front, they ain't exactly gonna be making money if you could just play your old discs instead of selling you the new remastered versions of these classic games, but it's also not as simple as 'they could run these games if they could read the discs', y'know?)
In an ideal world though, Sony's backwards compatibility would be on the level of Microsoft's. You can play 633 of the 1083 Xbox 360 games and 63 of 996 original Xbox games on both the Xbox One and Xbox Series X/S and it's literally just 'You own this backwards compatible game on disc? Cool, just pop your disc in and it'll download it to your console's hard drive and you can play - just remember you need to get the game disc in the drive to play. It's a digital game? Cool, you can just go ahead and install it and play it.'
And in an
ideal ideal world, Microsoft's backwards compatibility would encompass all 360 and original Xbox games, but you know rights issues, technical issues, and stuff like that. It's why they've stopped adding new games but like that's still a ton more classic games than Sony offers lol.