You answered your own question. "Mainstream" music is not meant to be talented, it's meant to sell an image and be accessible so millions of people with very little interest in actual talent and art will buy into it. Of course she possesses some talent, but it's nowhere near enough to merit all the attention she gets.
Take a look at Rite-Aid and Papa John's hyping the crap out of her new album. Mass marketing to appeal to the masses.
If it still doesn't make sense, then maybe this will. Artists like Taylor Swift are the McDonalds of the music world. Fast food is cheap, easy to make, easy to consume, and generally not very good for you. Same way with her music. It's accessible, watered down, and people can enjoy it without thinking too hard (or at all). It also doesn't help that she can't sing live.
I guess it just sucks that people like her and Nicki Minaj get all the attention when there are hundred of talented bands out there working their asses off who will never see anywhere near the attention she does.