If you don't like the car analogy, how about bikes? After all, kick scooters are parked in the exact same section of the sidewalk that bikes are (the "furniture zone"), and are frequently even locked to bike racks.
For example, in many cities once every week every bike parked in a public area is labelled with a little color ribbon. The colors rotate according to a fixed schedule, so that it can be verified if a bike has been parked for more than two, three, four weeks. If a bike has been left unattended for more than N weeks (where N can vary) it gets towed away. They all get stored someplace out of town, and once a month the bikes that haven't been reclaimed for M months get sold for cheap.
In other words, there are systems for how long you can leave your property unattended in public before it ceases to be your property.
The primary reason there's no system for handling abandoned bikes in the US is not that nobody uses bikes. Bikes aren't especially common, but the issue of an abandoned bike isn't going to come up -- ever -- because of the extreme frequency of bike theft. An abandoned bike will quickly be stolen, just like a non-abandoned bike. Bird's scooters don't have this problem because they're tracked. But the background reality of bicycles may contribute to jzl's (false) impression that you should be legally able to just take scooters that aren't locked down.
How much of an issue is bicycle theft in the Netherlands? How long would you expect to be able to own one before having it stolen?
This does not represent my experience at all, I've had bikes stolen once every three years on average. It won't surprise you that students learn to buy very cheap second-hand bikes with very big bulky locks really quickly here.
On the plus side, I've never been worried about junkies mugging me. They steal/sell bikes for drug money instead, and I honestly wonder if that is a uniquely Dutch thing.
Also, there's supposed to be organized rings where bikes stolen in Portland are trucked to Seattle (so they're much harder to identify as stolen) and vice-versa.
Sometimes scooters are parked on the side of the road. Sometimes scooters are parked in a ditch beside the road. Bikes rarely are.
Scooters can be parked at bike racks. Are there enough bike racks to park the scooters at the bike racks? would the situation be similar if all of those scooters were bicycles or if bicycles were as cheap as scooters?
Speaking from my experience in Shanghai, where bicycles are common, there's no such thing as a bike rack. (Well, I have seen racks for rental bikes. But none for individually-owned bicycles.)
Rather, supermarkets, university buildings, apartment complexes, and other places which are likely to receive a lot of incoming traffic have bicycle parking lots, and if you're somewhere else, you park on the sidewalk.