Check the profile; most account closures have a basic reason attached to them.
If that is not enough, or you need more details, you can open a ticket. You will likely need access to the e-mail account attached to that account for staff to provide you with any information.
https://support.chess.com/customer/portal/emails/new
Also, closed account content is normally kept as far as I know. Accounts closed for abuse just have the content hidden.
Thank you very much for the reply. 
However, I'm afraid it is far too late for me to have hope of learning anything whatsoever about this matter. I just discovered that the account has already been deleted, which means all information connected with it (including why it was closed) is probably gone. Still, the link you provided is greatly appreciated, and I did send a message to Chess.com support. If any enlightening information comes out of it, I'll be very pleasantly surprised and will have you to thank once again!
Assuming I don't receive a response within a week or so, does anybody have advice to offer on whether I should just abandon the site altogether? Chess.com is an awesome place, but if random account closings and deletions without notice are a regular occurrence, it may not be in my best interest to return...
Accounts don't get deleted. If you can't access it, message me the name and I'll take a look.
Already replied to that but it looks like your ticket worked and staff reopened the account.
I'm sure they messaged you about it and that you'll need to close this account or risk having both closed for having multiple accounts.
Had an account on this site for over 7 years, before it was abruptly closed yesterday. I have no idea why, since I received no explanation via email, and had never once been warned by Chess.com staff about any violations of site policy. I've always been well aware of the rules here, and would never knowingly break them, which is what makes the whole thing so shocking.
It definitely wasn't the result of cheating, because I had not played a single game. I can recall a few debates I was involved in, but certainly no occasion where I was intentionally rude (plus, I've seen many obvious insults tossed around by members whose accounts were never closed). I'm 100% sure that I've never spammed any thread, nor posted anything related to politics, religion, etc, nor ever attempted to advertise anything in the forums or elsewhere. I can also say with confidence that I never used any obscene language, either.
Of course, if I'd ever received a warning about an accidental breach of site policy, I would have gladly deleted as many of my own posts as necessary and made sure to avoid any such infraction in the future. There was a decent amount of content associated with my account (all of which is now lost forever, presumably), and I was even a premium member here at one time.
Does anyone know how I can find out why my account was closed? It just doesn't make any sense to me at the moment, and I feel like I deserve some sort of explanation...