Since the caves allows animals ie abu.
Probably because he was afraid of losing him. Plus I am not sure the Cave of Wonders would allow that.
How would Jafar get Iago to do it after seeing Gazeem get killed by it?
The cave told Jafar that only the worthy one, the "diamond in the rough" would be allowed. Iago would have been a chicken dinner.
Now thinking of it he says that and yet Abu who may not have been as worthy was allowed to go with him. Probably why the TC asks what he did.
Because there wasn't someone with him who was "a diamond in the rough".