DGEX is a niche exchange with low volume. it was released as the new top exchange over a year ago, especially for Nxt. But it has never reached its own standards. So, you don't need to wonder.
There are actually thousands of such exchanges so I wouldn't be surprised if another of them bites the dust.
NXT-E was also started about a year ago especially for Nxt, but became a zombie exchange, then went offline. I lost a tiny number of Nxt on it, but the writing was on the wall for months before it closed. It may be wise not to keep much on DGEX in case the writing is also on the wall for it.