No license is required to ride a bicycle, and I'd wager that a bicycle is more dangerous than a scooter, since it weighs more and goes faster. I think bicycles just get grandfathered in.

Not that I want licensing for bicycles or scooters, mind you! I bike to work every day, and it's indisputable that much smaller vehicles going much slower are way, way safer than cars and trucks. 37K people were killed in vehicle crashes in 2016, the most recent year for which I can find data.