It's possible Sony was more forward-thinking with their licensing.One thing I don't get about Backwards compatibility is, don't you need publisher permission to make them games backward compatible for new hardware. Don't Xbox have to get permission for each 360 game released on Xbox one?
Also possible that native playback at the hardware level changes things. MS is using fancy emulation that requires a bit of manual tweaking to get games working perfectly. So legally maybe they are not considered the exact same games as before? Just spitballing here. PS5 is sounding more like a PS2 situation where the hardware could just play your PS1 games natively.