> If I helped someone the only thing I'd expect in return would be that if the person I helped is ever in a situation where they can provide help to someone else, they'll remember the time they were helped by a stranger and take action.

You say that as if it's a minor thing ("the only thing I'd expect") but you might be expecting someone to risk their life, get accused of rape by an unstable person, put themselves in danger of injury or lawsuit. It's not a trivial matter. I personally wasn't expecting anything from this person I helped, I was just pointing out that she ended up being no different from the other drivers around her - just less fortunate.

As Anderkent says, on a basic level, we're all expecting "something in return". We help other people, maybe they'll help us one day. But this instinct is tuned to small communities (in which we evolved) where "paying it forward" like this is very likely to occur in a short space of time. You help me carry my kill home, you can have some of the meat. You help me get my harvest in, I'll help you raise that barn. But in large communities (several million strong, in some cases) these opportunities will be limited so we are more reluctant to get involved. We might not be consciously weighing profit and loss, but on a subconscious or instinctive level, we are.