Something I've never understood is why skateboards and mopeds and vespas?

Why aren't we all moving around on something small but stable like an electric fourwheeler/quad/atv or whatver you want to call it?

I've never received a good answer why the more stable, easier to ride, less likely to topple quad hasn't been adapted to city use or even made street legal, when mopeds and vespas are everywhere.

You can still park many of them in the space of a car and many more people would be capable of driving them. To me the electric quad seems like no brainer city vehicle.