Once you initiate a collaborative cancel, you can’t undue it.

So, imagine Alice initiates a trade with Bob and then Alice decides to initiate a cancel when Bob is unresponsive.

Then after Alice initiates a cancel, Bob says “sorry about that. I’m here now. Send the code.”

If Alice sends the code, then Bob can just accept the cancellation instead of acting honestly and Alice loses her money and Bob successfully scams Alice.