Why is my father in law so selfish?

I have been there for him and my mother in law whenever they need a a translator and favor but when I ask for a favor it's a problem. I am the type of person that refuse to ask for a favor or bother anyone because that's just me. My father in law came by to drop of a raisin bread and my 16 year old asked him can he take him to the supermarket and he got all shooked up saying I will take him but he needs to walk back. I live in Florida and the supermarket is a distance away. I have been too nice and this is how I get paid back, really? he is so damn selfish and can't do me a favor when I need one. I am so sick and tired of phony family members and that is why I have kept my distance from my brother. I know life is short and we need to move on forgiving but why are people so selfish? I have helped everyone I come across in any way I can and believe in generosity and paying it forward.