I suspect if you're wary about fomite spread of disease (later shown to be airborne for COVID but initially assumed), then it's easy to pick up a phobia of grappling the handlebars of a scooter that a stranger has recently used.

Additionally, at least anecdotally here, as the city centers hollowed out of normal business/leisure traffic, a lot of the rental vehicles were visibly breached and used by homeless folks, which often tarnished the literal appearance and reliability of the rental units in addition to damaging the brand.