Why is it that we tend to feel obligated to help people? Is it because we expect people to return the favor at a later time and date?

I have noticed with myself lately that I have had little desire to help people. No real reason behind it, just more or less a lack of desire to do much of anything other than spend time at home. Is it possible for people to do things with out expecting something in return. I remember when I used to help people just because they asked.

Why can’t people be people why just help others because of the satisfaction you get for being nice to others?