It turns out reality is slightly more complicated than raw game theory, which is basically just what you described.

To be honest, it sounds like you might be internally cynical and externally giving, and exhausted seeing the results.

Most of us quite frankly weren't raised to optimize our own social networks, but over time I've realized it's not that difficult to create a mutual understanding from which everyone can better respect/build themselves and each other up. (e.g. this favor you asked requires a lot more of me than it saves for you, therefore, it's an impolite ask and it's a no)

Frankly though most people don't think that far ahead. Without "training" or manners, the common man is generally prone to his selfishness. It's never been a secret or a revelation, but people enjoy their extremisms.