The 10 number is for literally one person, I'm also discounting their mass (this isn't a precision exercise).

If you add 5 people to the car, call it 80kg per person so your you goto about 2.2 tons, then the damage number would be about ~24, but divided by 5 you end up with 4.8 (so a fully loaded car does about half the damage per person compared to one with a single occupant).

The thing is of course on some level this is large scaling factors applied to small numbers - i.e. tires still don't fail that quickly anyway, neither do roads.

Conversely it is actually weird to see that on this one metric, numerous self driving EV taxis is actually better.