why? I do not understand.

For the same reason one wouldn't posit "liking Omega" as a good explanation for why someone would pay Omega in the Parfit's Hitchhiker problem.

Could you expand on this? I'm pretty sure that "liking the driver" was not part of my "solution".

I suppose my "honor module" could be called "irrational" .... but, it is something that the hitchhiker is endowed with that he cannot control, no more than he can control his sex drive. And it is evolutionarily a useful thing to have. Or rather, a useful thing to have people believe you have. And people will tend to believe that, even total strangers, if natural selection has made it an observable feature of human nature.