Weren't the scooter companies paying random people who signed up to go charge the scooters themselves at their homes? Surely that's far higher liability.

Plus, if this was a concern how on earth is the used car market able to survive? I just don't think liability factors in here at all. My guess is that scrapping them is easier and nets about the same amount of money as selling them. Selling that many scooters off piecemeal would take quite a bit of time & effort, plus costs to store them in the meanwhile.