Not sure if the CDI method is like the peptide coupling methods, but in peptide coupling methods only about 2 times excess amine to be reacted is utilized. The CDI overkill excess amine could possibly be to make sure that all of it reacts, as it's better to have leftover worthless amine rather than unreacted product, eh? (all methods have some ratio of over-excess amine, for this purpose, SWIM thinks.)