All the guidance that a self moderated community should need:
That doesn't work. Why? If we all agreed on what "Be respectful" meant, all of this wouldn't be happening.
But it's obvious that we don't all share a common definition of "Be respectful." Some people think it's respectful to use "he" as a default pronoun, while others do not. Some people think it's respectful to use the singular "they" in place of a known pronoun preference, while others do not. Some people think it's respectful to write answers and comments saying that transgender people are mentally ill and should seek treatment, while others do not.
And that's just for this one issue. Some people think it's respectful to copy/paste their entire homework assignment into the question box or to ask vague questions with no research, while others do not. Some people think it's respectful to write "don't be lazy just google it," while others do not.
We could do this all day, and basically have been for a couple weeks now. A system in which individual moderators take action based on their personal judgements is not a coherent system. Moderators exercise a great deal of judgement, that's what we elect them for, but there has to be some guiding document that goes into at least some detail on the norms we're all going to adopt, even if we don't entirely agree on all of them. Otherwise every moderation decision is just subject to the personal whims of whoever happens to see it.
As other questions have noted, a number of members of the community are on the spectrum. For some, it is more difficult to intuit social norms and culture, and clear social rules may be more helpful than vague principles. Similarly, we're a widely international and culturally diverse community, and social norms differ, so even among the vast majority of people here who aim to act with respect, everyone has a bit of a different interpretation of "be respectful."
Finally, "be respectful" opens up the giant question of intent: "well I didn't mean to be disrespectful, so surely I wasn't violating the code of conduct." The code of conduct puts the focus on the content, not on assessing whether the user posting it was trying to be respectful.
If someone needs more than two words to know how to behave, a thousand more is not going to make a difference.
If someone is determined to misbehave, then sure, no policy document is going to stop them. That's what the enforcement tools are for. But a code of conduct serves other purposes. It provides guidance to those who are genuinely unsure what is allowed and some sense of due process to those determined to break the rules. As the Contributor Covenant, adopted by many open source projects, states, a code of conduct is a statement that allows us to be "overt in our openness, welcoming all people to contribute, and pledging in return to value them." As such, a code of conduct is a public statement of the community's norms, which serves as a signpost to someone considering joining.