There is one company I'm aware of that at least operates here in Canada called Neuron, which has helmets attached to every rental scooter. You're told by the app to put it on.
That is, sadly, the main reason I've found people choose not to wear them. The one time I rode with that brand I didn't either, because it just looked...gross.
I'm buying my own e-scooter for when the snow clears. And a helmet.
Tier in Germany did have helmets on some of their older scooters, however it seems like they replaced them with newer ones which don't have them anymore.
There is one company I'm aware of that at least operates here in Canada called Neuron, which has helmets attached to every rental scooter. You're told by the app to put it on.