Cracking down on the scooters is relatively easy: there are a handful of major actors, and dealing with them solves the problem.

Human waste, needles, garbage on the sidewalk is the result of hundreds of bad actors, which correspondingly takes significantly more resources to deal with. (And on that note, the state of Texas is the worst offender. Their official policy for dealing with their homeless during the Perry era, and still their unofficial policy, was to give their homeless showers and then a bus ticket to SF.)