I think people change their looks because they want diversity and they want to express themself. Some people want to change their lifestyle or subculture.

They are some people who care a lot about how they look like , but there are people who dont really care about stuff like this. Some of them change they look to look fashionable or to be recognized in their community. Some of them just are boring of the look they have for a long time .   People allways find some reason to change they look.