Depends on the aircraft, current ultralights that you don't need to drop $100,000 to get licensed for can only weigh 250 lbs, while motorcycles don't really have a limit and can weight over 1,000 lbs, approaching the weight of a Cessna 152. And when you account for crash scenarios, yeah the rider is at risk in both, but the motorcycle is far more likely to be in and around other people and vehicles during a crash, while a plane is 99% of the time over clear land and even an emergency landing is unlikely to put other people at risk.

It ain't a perfect comparison, both have problems, but it is far easier to get a license to drive a truck hauling 20+ tons than to get a license to fly a 500 pound plane, and motorcycle licenses is basically a signature and a couple bucks away.