Sense of obligation, indoctrinated into us by belief systems underlying "manners", "religion", "judgments of good/bad". It's hard to break that and become autonomous. Oprah was quoted as saying she decided when young not to do anything she really didn't want to do, because it would be against her higher nature. Worked for her.
Because we just take what we get.
Partly: more powerful people set up conditions to enslave us, since we are captives of our stomachs and must eat
For survival. If we all just did what we want civilization wouldn't get very far now would it.