It's the same question as "why do people eat crap?" "why is it so important for everyone to get the newest iphone?" etc. etc.
The music market has provided the audience with some musics. People need to consume fake emotions in simple melodies, because they don't have real emotions in their lives. Same thing with romantic movies, specially Hollywood ones.
I must say there ARE some pop songs which are just fantastic, but it's not even a 1% of the crap that it's being produced.
The only aim of pop music is to produce/sell music and make money with it. The music market is just disgusting, just as the food market and everything out there which you are taught to want, although you don't really need it, let's not even talk about clothing industry, as nudists, I don't think it's worth mentioning it.
If people were aiming for true emotions, new universes of sound, they would AT LEAST question the music they GET from the market, and go and explore other horizons.
I'm not saying that pop music is bad in itself, I'm just trying to explain your question "why is it consumed?" and the answer is: because this music is meant to be consumed, not to be listened, nor to expand the minds of the listeners through amazing sound proposals.
Do I sound fascist by saying this? It's not my intention to hurt anybody's sensibility. I respect that people LOVE pop music and almost only listen to that, because I know that it was not only their choice, they "got it" and they "took it". Now though, to change this fact IS our choice indeed :D it's never too late to discover new worlds of sounds out there :D