Those other passengers will presumably be people who know the pilot,
and can asess the risk accordingly.
... but what does this have to do with how much the pilot pays?

Because if the pilot has to pay for the flight himself, he won't be
carrying complete strangers (no incentive) and thus exposing them to
risk. Therefore, to take away the pilot's incentive, he's made to bear
the entire cost. It really does make sense.

Michael