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There isn't any rule against editors checking site status, so long as information doesn't breach confidentiality in some other way. And some editors do give status information to some people who ask.
I worked for several years on multiple attempts to see if something like that could be made to work. I'm persuaded that even if there were no harm, the rare occasions of actual useful information being available to be given, simply don't justify the overhead.
But you don't have to take my word for it. The results of the largest attempt to give status reports are still publicly available: anyone can read a thousand of status checks there, and see for himself if even one out of a thousand suggestions has associated information that an honest person could put to any conceivable use.
I used to answer people who were asking about their site's status, but I soon learned that if their submission had been rejected and I told them so, they became hostile and argumentative to me, despite the fact that I wasn't the one who did it, regardless of how good a reason there was for rejecting it (it was a mirror of their main site that already had a listing, it was a forum with three posts in it, etc.) On the other hand, if it was still waiting for review and I told them so, they would often either pester me to go and add it myself right now, which is annoying; or else they would press for irrelevant details, like whether their site was near the top of the queue or not (information that has little if any bearing on when the site will get listed.) I really can't think of even one time I was able to give a submitter information that he or she didn't already know ("It hasn't been listed yet, and I can't predict when or if it will be.") And people tend to get frustrated and nasty if you can't give them information that they didn't already know. It's a lose-lose situation, and any time I spend on it would be better spent adding a new website to the directory and potentially actually pleasing some webmaster out there. :-)
The fundamental issue of courtesy, that your mother taught you before you went to kindergarten: "what would happen if everyone did this?"
The fundamental issue of fairness, that an editor always has to consider: "is it fair to reward discourtesy? is it fair to let an interested party influence priorities?"
The fundamental issue of efficiency, also a consideration for editors: "what activities contribute most to building a directory?"
I used to answer status questions, and tried to find a systematic way of answering them fairly (that is, giving consistent treatment to people that asked, and giving fair treatment to suggestions that weren't asked about.)
That much we could do. What we couldn't do is justify wasting time on it, either from the viewpoint of editors or of honest submitters.