So yes, Lon did leave the cupboard pretty bare with his actions. Maybe he could have kept Kur based on that timeline? But with all those feet int he water, you are weeks behind everyone else in a recruiting pitch.
There are portal entries and transfer announcements--two very different things. A player can enter the portal just to test the waters--one could argue that's the wise thing to do with a new coach incoming.
Reaves was leaving. No incoming coach is going to convince an NBA-bound player to stay.
Victor Iwuakor likely knew Moser was hired when he decided to transfer. He announced he was going to UNLV after Moser's hiring, but only a couple of days.
Alondes entered the portal nearly two weeks after Moser was hired and did not announce his transfer till five weeks after that. Moser definitely had time to try to convince him to stay.
Manek entered the portal the same day Moser was hired, but his transfer announcement came nearly two weeks later, so Moser had time to convince him to stay. Moser says Brady was set on leaving and maybe he was, but at the time we were all holding out hope that Brady would leave the portal and return to OU. Were we all in denial? Perhaps.
Moser also had time to reach out to Harmon. Was Harmon even considering returning to OU? I don't know but Moser did have time to convince both Harmon and Kuath.
I've acknowledged that it's difficult to hold an incoming coach responsible for departures, though it's always job one for him to try to do so if he's taking over a team that's even decent. It's something a fan can hope for, but shouldn't expect. Time-wise, Iwuakor and Reaves (whom I've never mentioned as a player Moser could have retained) are the only guys who were lost causes. Manek, Harmon, Williams and Kuath all left 12 days or more after Moser's hire.
So I'll say again, when Kruger left, the cupboard was far from bare. It's in no way on him that players left after he retired. He reportedly reached out to encourage them to stay, to assure them that Moser was a quality coach. That's all he could possibly be expected to have done.