Biased or normal behaviour of MIL?

When we first got married, my hubby insisted that we stay near my in-laws who are retired so that they can help take care of our kids in future. My MIL also said that we should stay nearby. But one day, even before I got pregnant, my MIL suddenly said that she don’t want to take dare of my kids because she is tired and wants her “freedom”. But she was ok taking care of her daughter’s kids aka my sister in law’s kids. Even when my kids are sick now, my MIL also never offered to help out or do anything. My own mother who is still working had to take leave to help me out. Is it true that a daughter in law will never match up to a daughter? Feeling so tired and disheartened...