But you could come up with a believable reason for multiplayer. (Ex. Maybe the devs decided their servers wouldn't scale and had to move to Sony's, but those require users to have a Sony account.)

For single player, there's not even a hypothetical excuse. They just want you to be inconvenienced for their own gain.

Not justifiable but one can weave some twisted logic to explain it. With single player games there is even less explanation.