I don't know the full story. I hadn't visited in years, and it just so happens that something reminded me of it, prompted me to try to look up some of the old ytmnd memes for old time's sake, and in turn find out that it died this past week.
It seems that it unexpectedly went down early this week, and the culprit seems to be that it's database was wiped for some reason. The site has been in decline for several years now, and I read one comment claiming that they'd read that the latest full backup was from five years ago.
From what I understand, the owner is pretty much done with hosting the site. However he's exploring what options that he has to restore data for hosting in an archived state. I also believe that there are a handful of other archival projects that were working to keep some of the classics alive.