This question was asked by my 6-year-old grand-niece. I gave her a serious answer. I did not get offended. She's only six, and just trying to understand.
I told her that for me, at least, it's because it's so easy to take care of. It is easy to wash, and dries quickly, so I don't have to take time to fix it or go around with wet hair. I don't always feel well and I don't want to spend my energy taking care of my hair. She seemed to understand that and the conversation moved on.
What if we could all be so guileless? I don't understand that, so I'll ask about it. Maybe I'll learn something. Maybe I'll gain a better understanding of that person, or of some other aspect of life. Maybe it will lead to me liking them better, or the other extreme--to inwardly shuddering and moving on. Maybe I'll offend someone, but maybe they'll actually be glad I asked. And maybe, just maybe, I'll gain better perspective and be less judgmental.