Did Boba chicken out?
He would have known that Din was ultimately seeking a Jedi to hand Grogu over to.
It was rather convenient that Fett was somewhere else, nobody explained where or why, the whole time Luke was there (not to mention when the dark troopers were reboarding the cruiser).
Maybe he's traumatised by first seeing a Jedi cut off his dad's head and then being humiliated by Luke at the pit of Carkoon.