But... This is not what smart delivery is, what you are talking about with the smartphones also already existed on consoles, heck moving from an xb1 to an x|s preserves all your settings just like "moving from an old iphone to a new one", but that's not smart delivery.
Smart delivery is what ms calls having the most suitable version of the game for your system, this causes the game files to update instead of downloading a completely different version.
Games with smart delivery then make it impossible to have several versions of the game because it is seen as one version. This is why you can't have to xb1 and x|s versions of the game at the same time, whereas a ps5 version will always be seen as a new game, so you need the ps4 version as well to do save migration if needed.
And because it's seen as only one version with smart delivery, your save is required to be compatible; if the dev can't make that work then they can't implement smart delivery.
You also missed out one more step on the PS5, you have to go into the store and "purchase" the PS5 version, albeit for free when it works, otherwise you will just continue playing the PS4 version for all eternity.