How come the Sport Pilot rating requires only 20 hours of instruction, as opposed to 30 hours for the Recreational Pilot, or 40 hours for the Private?
There’s less to teach a Sport Pilot. Since you’d not be allowed to fly at night, night training is not required. Since you wouldn’t be flying by reference to flight instruments, no instrument training is in the curriculum. Since an LSA can’t go as far, cross-country flights need be only 25 miles (as opposed to 50 for the higher ratings). And, since you’d be restricted from flying in heavily regulated airspace, no training is given in procedures used within such airspace.
