Well they do stop, and they have their reasons of course. But why? Good Samaritans? Well maybe, but most people would suspect it's for the company. You're driving alone, and here's someone to talk to, and hey, you can help them out at the same time, why not. Certainly there's a question of predisposition, you don't debate the issue with yourself on the spur of the moment, or if you do you've long driven by before you draw a conclusion (possibly muttering regrets to yourself about not having lent a hand).
Well company is certainly a prime motivator in many ways, but it is a little too simple to leave it there. When I read Mario Rinvolucri's wonderful treatise on hitching though, it opened my eyes to something I'd not considered before.
Consider this: the relationship that hitch-hiker and a hitch-hikee share is rather unique - unparalleled in fact. I can think of no analogous situation. The relationship is reliably transient, you will in all likelihood never see one another again. It's reliably anonymous, only slightly more so in the one direction than the other (the driver does have licence plates, but few hitchers note them down after all).
There's almost no face to face contact, the driver at least focusing (one hopes) on the road. Entering the car involves an unusually restricted and fleeting view of one another through a car window or passenger door. I've often registered subtle surprise at our respective appearances (or sizes) on those odd occasions I suddenly stand face to face with a driver due to a toilet or petrol stop on a long shared trip.
The relationship is tangibly tinged with a feeling of debt on the part of the hitcher and of righteousness on the part of the hitchee. The latter extending a perceived favour to the former.
Conversations tend flow on account of a feeling that they should, the hitcher feels an obligation
