they dont port old games to other consoles, they do remake and remasters. I think remastering older games makes a lot of sense, but there no ps3 game that gets ported to ps5 its always a remake or HD release. Even games like last of us on ps4 was an HD release for ps4 not a straight port. I can't really think of any old games that just got ported to new hardware with there old engines / graphics. This falls under the remake / remaster category. Not to mention to coding issues that would arise from just trying to port an old game to a new engine, that's why they basically have to remake the game when its been that long. It's worth noting that remakes is an intended feature as well, but it will have different needs that you will have to meet. As opposed to just doing a bit of light code to a game to make it work on another platform you will need to add stuff and upgrade to a new engine and do more choices / work to create a remake, which I honestly think is realistic to reality.
Even in the past few weeks we have seen cyberpunk launch on old and new platforms and they are completely different games. Cyber went the other way with it though they made the quality game then tried to downgrade it to work with xbox / ps4 and its having major issues. Typically they go from the weaker hardware to the better but cyber was special case and it's really hurt them trying to do it that way. Which they are only doing due to release timing, had it been another 6 month delay and no pre-orders they would likely just of made the ps5 / xbox X versions, but that's a different topic all together :)