Why?

Why is it that publishers are really pushing marketing novels by slotting them in to boxes?
I am tired of finding a novel which looks right, the blurb reads enticingly well, but when I read it I find it's not at all what the marketing promises.

I've thrown several novels back at the librarian with a snarl recently, because they promised to be historical novels, but turned out to be Romances. No, I don't mean a novel with a romantic relationship as a subplot. I mean the darned thing was a full blown Romance with a pretty historical setting. Yet it was marketed as a serious historical novel.

There's a trend to market literary historical novels as if they were genre romps. I'd have missed several excellent novels if I had studied the blurb and not listened to my friends.

Why do publishers think we all want candy floss reading? Why do they market well written, challenging novels as if they were easy reads? It puts readers off.