First off, you're not the one who started this thread, so who are you to judge? Second, I did say in my very first post that the real answer was probably unknown.
Besides, sometimes the right "answer" to a question is that the question itself needs to be reformulated, that it's based on an unexamined assumption that isn't necessarily valid. This particular question, about the reason for the name change, seems to be based on the assumption that there needed to be a reason, that Roddenberry was initially committed to Yorktown and something had to happen to make that change. But early ideas are often quite rough, or are simply placeholders until you can come up with something better. And understanding that broader principle can be useful not only for this question, but for other questions about the creative process.
Given how many possible names we know Roddenberry went through for the captain before settling on Christopher Pike just days before shooting the pilot, I would think it very likely that he had a similar list of multiple possible names for the starship. He probably just put Yorktown in the pitch document because he needed to put something there, or because that was the one he happened to be leaning toward on that particular day. And it wasn't the only name in that first proposal that was changed; others included Captain Robert April and navigator José Ortegas, not to mention the "telecommunicators" (and of course the line about how the ship "rarely lands on a planet"). Why did he change any of those things? Because that's what often happens to first-draft ideas. Because what he put in the pitch document wasn't a refined version of the series concept, but only a rough approximation, an early stage of a work in progress. And that's most likely the real answer to the question -- but it's an answer that requires some background discussion about how the process works.
This. Writing a series is a challenge that most people would/could never take on, primarily because the time and energy required for a such project is enormous. Most of my writing experience- excluding any writing I have done as part of my career- is limited to fan fiction, as I don't have the ability or the self-discipline necessary to write anything worth publishing. For me, one of the most challenging aspects of writing has been the creation of new characters, as I've often struggled with simple concepts such as their names, backgrounds, likes/dislikes, etc.
I've changed character's names several times before making a final decision. I don't pretend to know what Gene Roddenberry was thinking when he chose the name
Enterprise, but I would imagine that he wanted to choose a name that would not only catch the attention of the television audience, but would also endure.
Yorktown doesn't capture the imagination the way that
Enterprise does.
It's possible that I would feel differently had Roddenberry kept the original name, but even looking at each name objectively, it seems clear that one is more awe-inspiring than the other.
