I agreed with you. Sounds unnatural, though it makes sense.
If say "為什麼人喜歡...", maybe they're having a serious talk. It's just my feeling when I heard it. For example, 為什麼人總是喜歡做些浪費的事情? In this situation, I would say like that.
Is 自拍 strictly a verb? Or can this also be translated as "Why do people like selfies"?
I always thought it was a noun and that "take a selfie" would be "拍自拍“ even though it's redundant. Is that correct?
Good question, in my opinion are both right. The words in Chinese aren't divised strickly, some words can be both verbs and nouns. So I think, you can say "selfies" or "take a selfie", it doesn't bother Chinese speaker. For us, it's the same.