I think the main thing that is to blame for the loss of users and popularity, would definitely be the ticket response times.
Like Lemona said, if I were to come back to this website and not be able to sign into my account, I would expect a reasonable wait time for such a thing to be handled. Especially considering the fact that xat did this intentionally? They should've been prepared for the tickets.
Of course, I suppose you could say this is an effect of November 2015 and you could put all of the blame there and on the hosting company that allowed it to happen.
But xat Admins are also to blame, for either not wanting or not caring enough to fix these problems that everyone in the community experiences. After all, they have the final say on what goes on here on the website they created.
If nothing changes, we as a community will continue to see the active user base dwindle, and eventually xat won't be open - you can't pay the bills without the users, the ones who buy powers, xats, days, etc.
Maybe I'm just being nostalgic, but I miss when I could load up the homepage and see a promoted chat full of users talking to people that 9 times out of 10, they didn't know.
Now you go on any promoted chat, and it's rare to see 15+ users. I'd consider that a good day for xat - but even then, these chats are quiet; nobody really talks on them anymore.
I've been registered on xat since 2009, and these past few months I've seen nothing but the same users around on xat, on almost every chat I go to.
The admins should not be afraid to fix these problems, as the future of their website depends on solving these issues.
I hope things change in the future, such as:
Ticket response times
Active volunteers (goes hand in hand with the first bullet point)
TL;DR - We need change.