As for straps, they can actually pose a problem, particularly with the clean. For countless lifters, straps keep the bar from sitting far enough back in their hands when they receive the barbell. This prevents their elbows from raising up, and the result is a poorly positioned barbell.
However, many olympic lifters use straps for their snatch workouts, in order to “save” their hands for competition. It is much easier for the bar to remain in the proper position in the snatch (with straps) than the clean.
As for keeping the hook grip on the bar, some lifters “let go” of the hook grip as they receive the barbell, but others do not. This is a comfort issue. In all seriousness, once the hook grip is practiced, it does not hurt at all.