My last session of crawling over broken glass, to submit to 60 agents, took about two weeks. I prepared different query letters, synopses and writing samples to satisfy the finicky requirements of different agencies. There's no such thing as a publishing industry standard format for submitting.
Although I spent masses of time beforehand, researching up-to-date information on the likes and dislikes of individual agents, trying to target the right individual, I still feel that getting a positive response is largely down to luck.
By that, I mean one could submit the most perfectly edited manuscript of an imaginative, well-written story, but if it doesn't speak
to the person reading it in some way, then it'll go nowhere. There's so much that's unknowable about how agents select which projects to take forward. If they've just committed to a novel with a plot that's similar to yours, then bad luck you!
Another aspect of querying, which rarely gets a mention, is that many agencies use readers to do the first trawl through the slushpile. They're expected to identify potentially publishable (marketable!) material, but they have to keep to a certain work rate. Your manuscript might receive a cursory, and jaundiced, skimming before being chucked into the waste bin.
As for asking agents who ignored me, or who rejected me, why they were stand-offish, that feels like asking a woman why she won't go out with me. I wouldn't expect a totally honest answer, more a half-hearted series of platitudes. The truth of both scenarios might simply boil down to a reply of "I just didn't fancy you."
While I'm on this tack, I'm reminded of an old joke:
A disgusting old man hangs around street corners, asking every woman who passes by if they'll go to bed with him. He's unwashed, ugly and has no money, but still, he tries it on with desirable females. One of his friends asks him, "You've got a lot of nerve, don't you get your face slapped a lot?"
the man says, "but I also get to go to bed with quite a few women."
The moral of the story is: if you don't ask, you don't get.
Hence, like the dirty old man, I'll be persevering. Will I query agencies who've previously rejected me? Of course!
(I have no shame....)