Other mistake: When Abbott and Costello are bringing the first crate (Dracula) into the house of horrors, Abbott tells Costello twice to help with moving the crate. The first time Abbott says to help pull the crate, which is correct. The second time, Abbott says to help push, even though Costello is still pulling.
Other mistake: During opening scene, two faces of Big Ben show different times. One face shows 8:00 and the other shows 9:00.
Answer: The monster may have seemed obedient, but its overall behavior is unknown to us. It's possible that it was at times defiant, obstinate, or just didn't follow instructions completely or competently. It's also just a plot device for a silly movie. There has to be some reason, however flimsy, why Dracula wants Wilbur's brain.
raywest ★