Why do people dye their hair?

There are so many 名人 and regular people out there who dyed their hair. I like my natural hair color a lot. No need to change it into anything else. I just wanna know why, that's all. I know that 名人 sometimes dye their hair to get a new part 或者 to avoid being identified with their characters. There's not that many male natural blonde 名人 out there who remained blondes, yet at the same time there's plenty of dark haired female 名人 who dyed their hair blonde. So, brunette girls want to become blondes, but blonde guys want to become brunettes. That's a very strange phenomenon, at least to me. But why do people, even the regular people, dye their hair in the first place, that's a total mystery to me. Anyone?