The Mandela Effect is a big topic, and there are many possible explanations for why and how it is happening. I do my best to give you one possible explanation, as I understand it, that has helped me to deal with the changes that are taking place.
Whether it is changes in popular culture that are changing for you, or other, bigger things (such as the passing of people that have, apparently, never happened), things ARE changing, and those of us that have experienced the Mandela Effect for ourselves are simply trying to answer, “Why?”