About 4 keys will start 90% of the airplanes that even use keys
Like boats, most people don't know how to operate them or what to do with them if they do steal one.
Outboards and inflatables are what get stolen.
Then there is the "drunk late night regatta party" where people take the first dinghy they see and then that dingy's real owner swipes another one and so on and so on. They all get sorted in the morning though.