My mom is currently visiting me and my wife. This is her first visit since we moved here three years ago. She is not one of those intrusive MILs, but my mom and my wife just do not enjoy each other at all. If I wasn't married to my wife these are not two people would would ever willingly be in the same room.
My wife thinks my mom is rude because she made no effort to get to know her or interact with her. My mom thinks my wife is entitled for being at our house too often (when we were engaged), and expecting her to take an interest in her. My mom also (I think, worst communicator ever) was hurt that we spend more time with my in laws, so she began to really shut us out of her life.
There is also leftover resentment from our wedding. My mom to this day believes our wedding was an intentional set up as we invited a man she asked us not to (close friend of my dads, business associate of FILs). Because we didn't tell her he was coming she is convinced it was a plot to humiliate her. My wife thinks my mom is a spoiled brat and should have had zero say over our wedding.