I believe that it is because Peter was totally embraced he is horrified when the cock crows again. The ongoing statement of Jesus is that he does not simply offer us theories. If he says it he does it. If he believes in healing, he offers healing, if he believes in miracles he offers miracles, if he believes in serving he serves, if he believes in loving, he loves. One of the reasons why Jesus does have such credibility is that he really does do what he says.
Tonight is probably one of the best examples.
For Jesus takes his place at the table and the disciples are with him. It is not the select few. It is not just those who have never given up. Jesus knows that every one of us will fail and yet he loves us. Jesus then takes the bread and when he had given thanks, he broke it and gave it to them.