The problem though, is that scooters have terrible dynamic stability in comparison to bicycles which thanks to conservation of angular momentum and large wheels

The problem though, is that scooters have terrible dynamic stability in comparison to bicycles which thanks to conservation of angular momentum and large wheels, are very easy to control and remain upright on when traveling at speed. In contrast, even small things like hitting a small rock/bump the wrong way can destabilize someone on a scooter and lead to an accident. Falling off a bike/scooter at similar speeds obviously ends with similar results, but I'd be confident to wager that the probability of an accident is a lot higher on a scooter due to the point above.