If you can tell the renter did the action

But you can't, without onboard video, anyway. Anybody wanting to steal or vandalize a scooter won't do so on one for which they are (or just were) an active renter.

  by locking the devices the likelihood of them falling or being in the way is low

I don't get that at all. All locking does is prevents unpaid usage as a scooter; it doesn't prevent theft, vandalism, or bad acts with it (e.g. piling a bunch of them in the CEO's driveway as a protest).

But why as a renter would you want to only vandalize / steal the scooter that you just used, vs just stealing / vandalizing the hundreds of other scooters out there? It lets the companies collect statistics on who is more likely the doing the bad behavior, careless customers or random assholes?

The biggest complaint with these scooters is they are in the middle of the right of the public right of way and laying down on the street in an inefficient manner.

If they are locked to something, they would be outside of the right of way since lock points tend to be on the edges of sidewalks. If you put the lock on the correct point on the scooter, it will be fairly difficult to knock them over, vs the light tap you need today.

Locking also reduces the instances of impulsive bad acts, since now you need some sort of specialized power machinery to remove the items. And barriers to impulsiveness is a big factor in reducing crime. Did you know for example crime tends to happen more at the bottom of a hill vs the top of a hill? Because people don't want to walk up hills because it's extra effort.

On top of that, nobody has been complaining about personal bike ownership, which today follows a model of being locked to things.

JUMP bikes in SF for example follows this model, has been around before the scooter boom. I haven't heard a single complaint about them other than positive complaints such as 'why aren't there more?', and 'why are they restricted to an area?' The scooters on the other hand have had a bunch of negative complaints.