Agents, editors, and publishers clearly specify what they're looking for. Then, most aspiring authors ignore those specifications and do exactly as they please. You can post whatever you want on your website or social media profile: "Seeking young adult fantasy and memoir." Leave absolutely no room for misinterpretation. Doesn't matter. You'll still receive reams of poetry, travel, and self-help. Or whatever. People just don't care. See transom, vault right over.
I'm guilty of this myself. In college, a friend and I wrote a Seinfeld script. We put a lot of work into writing it but not an ounce into figuring out how one gets a television script considered. We didn't even know that we'd need representation. Naturally, our masterpiece was rejected without even being read—along with the cigar bribe we'd stuffed into the envelope.
(Don't feel bad for us. We got off easy. Without our contribution, Larry and Jerry were forced to go with that jail finale.)
I've written before about how the blacksmithing reality show Forged in Fire is an excellent learning metaphor for the writing process. What works for those blacksmiths will probably work for you and the book you hope to "forge."
Forged teaches us the importance of parameters. One of the most common mistakes on the show is the failure to meet them. In every other episode, an experienced blacksmith will produce an objectively superior knife...only to be disqualified because it's half an inch too long. Or it doesn't have the right serration along its edge. Minor, fiddly details, sure, but the parameters are explained at the top of every show, and each blacksmith has a Sharpie to write them down. The other smith's "knife" might be little more than a blackened lump of steel, but if they remembered how to use a ruler, they move to round two.
First, meet parameters. This is the easiest win I'll ever hand you. "But my thing is so good it won't matter!" No, it isn't. Even if it were, the gatekeepers will never know. There are too many projects to consider—it's simply unmanageable not to filter out the stuff that doesn't meet arbitrary specifications. If you expect their time and attention, respect it by following their instructions.
Of course, there's more to meeting parameters than using the right font or submitting in the right category. Every genre has its unwritten rules. Learn them well, especially if you think you're talented enough to break them. I can't tell you how many people I've met who want to write business books without ever having read one. Genre conventions are parameters, too, and the Picassos who successfully defy them only do so successfully because they mastered them a long time ago.
p.s. Dave Crenshaw and I chatted on his podcast recently. Take a listen: