"Why do people like taking selfies?"
However I do think Duolingo has a mistake here...
We would say 为什么人们喜欢自拍（Why do people like taking selfies）or 人们为什么喜欢自拍, and not 为什么人喜欢自拍 (Why do human beings like taking selfies)...Because the meaning of 人 in the latter sentence is referring more to human beings (the species), so it sounds weird...
Its weird because its inaccurate, 人 is translated as mankind or human beings whereas 人们 as people. Another possible translation would be 为什么大家都喜欢自拍？ although 大家 is really everyone.. 为什么人们喜欢自拍？ is not accepted currently.
I tried to report the translation but the only report choices were 'The audio does not sound correct.' or 'The dictionary hints on hover are wrong or missing.' or 'The English sentence is unnatural or has an error.' I can report inaccurate translations or even variations of accurate ones.
Does anyone else have the same problem?