Because a mono doesn't maneuver as easily. IF you get the line caught in the prop, damage done could be the same regardless of the boat, its just easier on a cat to keep it where you want.

The other issue can be getting it caught around the keel. Wind plays a factor as well.

Best bet is to pick it up from the bow - only reason we've ever picked up from the stern (as close to port or starboard side as possible) was due to us not having a usable boat hook.