The simplest and most likely reason is just because they don’t have to. Playstation is leading Xbox by a lot this generation (so far, things can change) and PlayStation just has no incentive to add value to something they’re already selling record numbers of. Xbox is trying to attract customers, customer playstation has left on the cutting room floor, and backwards compatibility is a way to do that.
I’ve had better luck with Tidal’s recommendations. Spotify just kept playing me covers and live music on my weekly and it was driving me crazy.