I think it's worth noting that some non-dystopian books have been popular in the last few years. John Green sells well and his books are basically all set in modern America. Similarly, books like If I Stay, Eleanor and Park, and Fangirl have sold well without containing any dystopian elements. And there's a fair number of fantasy novels aimed at YA readers (Miss Peregrine's Home for Peculiar Children, for example). Though the dystopian novels certainly seem to be at the forefront right now, other genres are still achieving some level of success.
It's also worth considering when these books were published.
Uglies- 2005
The Hunger Games- 2008
The Maze Runner- 2009
Divergent- 2011
Red Rising- 2014
Uglies was published a few years before the dystopian 'trend' began. To give a sense of the timescale here, it's worth pointing out that the first Twilight novel was published that same year. The first Twilight movie didn't hit cinemas until 2008, and we know that around that time, the popularity of the series created a surge in the number of YA 'supernatural romance' novels appearing in bookshops.
Speaking of which, some of the books that were marketed as being Twilight-esque had actually been published before, but were given new covers emphasizing the elements readers seemed to want. For example, The Vampire Diaries were mostly published back in the early nineties, but because they offered similar elements to Twilight- vampires, teenagers, a love triangle- they were marketed towards that audience, and got a TV adaptation. You could argue that Uglies has benefited from the success of The Hunger Games in a similar way- although its storyline seems quite different, the publisher can still sell it as a dystopian novel.
I'm guessing the current trend is largely due to publishers realizing that they had a hit on their hands with The Hunger Games and pushing similar titles towards readers. I imagine we'll have a new 'trend' appear within the next couple of years. The popularity of these books can probably be attributed to readers wanting more of the same (especially when they're waiting for the next installment of their favorite book or movie series). I'm sure there are other factors driving it- teenagers seem to be more active about social justice issues online these days, and I'd imagine that books about oppressive societies would appeal to those interests to some degree. And obviously these kinds of stories can make for successful action movies- more than the contemporary romances that also seem to be popular amongst YA readers.
But I think it's also worth considering that these kinds of 'phases' exist in adult literature too, it's just not as noticeable because adult books take up more of the bookshop, which allows for more variety. After 50 Shades of Grey sold well, a lot of erotic novels about dom/sub relationships seemed to pop up, with names like Eighty Days Yellow. One of the current bestsellers, The Girl on the Train, seems to be aimed towards the Gone Girl crowd- switching perspectives, the disappearance of a seemingly perfect woman, even the use of the word 'girl' in the title. The Accursed Kings series fell out of print, but seems to have been saved by the success of Game of Thrones.