Book publication is a business. As such, publishers publish what is selling best. This leads to trends. Remember all the Twilight knock-offs? Heck, I achieved first publication at the end of that one!
As a reader, it can be crippling though. You can be so over the angsty vampire and find that’s all there is in the New Releases. What’s a reader to do when faced with the endless parade of sameness? Go lateral. Go back in time. Go over to Goodreads and check out the many lists of book recommendations based on preferences. Want fast & funny? Slow & romantic? Running wild through spaceships butt-naked with all ray guns firing? Yep, they got that too. Goodreads is the place to be for readers who prefer a buffet, like me.
Go check out new ePublishers. They have more freedom to go crazy with variety. Over time, it seems each will come to specialize in certain kinds of books. This is in response to what their readers by the most of and what kind of good stories authors bring to them. Don’t be afraid to shop around. You never know what little gem you’ll dig up.