UI doesn't change because UI folks have nothing to do, it changes because people love to complain, and sales loves to be able to tell customers "we made that change you asked for".
If you like an app and don't want the UI to change, tell the company. as long as all the people who like it are silent and all the people who don't like it are complaining loudly, apps are going to keep changing.
Sure, because you don't know if the 900 people are silent because they're happy or lazy. A 10% complaint rate feels quite high for a typical feature and would tell me that I probably got something wrong.
If you like an app and don't want the UI to change, tell the company. as long as all the people who like it are silent and all the people who don't like it are complaining loudly, apps are going to keep changing.