I'm a human in America and that's certainly not the "unquestionable" default mode that everyone operates on.

Is it really unquestionable?

Sounds like you're conflating scammy behavior with behavior that furthers one's goals. Just because something someone does furthers their agenda doesn't mean the person they interact with doesn't also get something out of the interaction, and it doesn't mean they were deceived in any way.

Even in human interaction amongst your closest friends and family, they only interact with you for their own benefit - that just happens to be in pursuit of the endorphins/dopamine gained when they spend time with the people they share memories with, and it happens to be reciprocal.