Daughters-in-law and mothers-in-law: why must they often undermine and sneer at each other?

because a lot of mother in laws are controlling, and feel no one is good enough for their son, but don't mind who marry their daughters, they are being "taken care of", and I also think its some stupid form of jealousy as warped as that sounds....I have a mother in law of 27yrs. She was a beoch to me then, and still the manipulating wanna be control freak, who I have nothing to do with. Kissed her behind for years, then when she tried to pull some crap, put her right in her place. I did not marry my husbands family, married INTO it, not TO, so there is no law I have to be around anyone who is not good for my physical, mental or emotional well being....Some are "draining" people, love chaos, gossip, and are just not fun to be around. I can't stand the gossipy crap, at home, work, wherever....And the games people like to play, they set up the rules, in their favor, and I refuse to participate. Life is way too short for that crap....Some daughter in laws are just like what I wrote above. They are the trouble makers.....Just very immature people which ever they are.....