Why do mil's & daughter in laws clash?

BB
It seems like a popular thing for women to not get along with their mother in laws. I know it's possible to have a good relationship with them but it seems like a certainty sometimes for there to be excessive disagreements. When we marry/ are in a committed relationship how do we get along with our husbands/wives but not always their families? The people who raised them and played a major role in who they are? For instance I adore my husband, he is my polar opposite but we are perfect for each other and we love each other but I can.not.stand. his family!!! His mom always has some passive agressive stab to take at me or my parenting style, & they complain about anything they can. When they're in town they complain about the restaurants we take them to , I can ask over and over where they want to go & they say they don't care but in the next breath make scenes in the restaurants, pick at the waiters or complain that their meal wasn't 5$ 🙄🙄. I just want to know your opinions on why you think it's so easy to clash with our in laws? Or if you do have a good relationship with your in laws why do you feel it works?