Why do we have the time for other peoples children but not our own?

ok. kind of a long story but i am so jealous of my mother inlaw. she does EVERYTHING for my daughter to the point i may aswell be just the person that provides for her and his mother gets all the fun. its caused so much trouble that i don't like my partners mum no more and to but it frank i see her as an over baring cow. i think my issues with her are not relevant to my question as she does spoil her too much and buys her things that is totally out of my range. (it may sound petty but seriously its ridiculous i feel like i should just hand over my daughter for her to bring up) but i have tried to be reasonable. it came into my head that when i babysit my friends children i tend to do something with them, not that i don't with my own daughter but i make more of an effort with theirs. with my daughter i let house work and everyday life bog me down. i do stuff with her obviously and we have a routine of baking cakes together on a weekly basics ect. but my question is why do i/we make more of an effort with other peoples kids when we have them than our own and let daily "crap" get in the way?