Several things you have to remember. First, usually captured Clan warriors spend time as bondsmen before becoming a warrior again. They need to prove their worth and loyalty to their new Clan before having their bondcord cut. They aren't likely to be given the opportunity to do so until after the current battle is over. Some bondsmen are never given that opportunity, such as a freeborn captured by Clan Smoke Jaguar which doesn't allow freeborns into their touman. Second, there is a chance that in the process of being defeated that they are injured further delaying their return to combat. Third, their standing with their new Clan helps determine which unit they are assigned to which in turn helps determine how likely they are to have a chance of entering combat and earn personal glory/honor. A Warden warrior captured by a Crusader Clan is more likely to be assigned to a lesser unit away from combat. Fourth, if a warrior is repeatedly captured by another Clan, then sooner rather than later people are going to question whether that warrior is (a) worth the effort and (b) worthy of becoming one of their Clan's warriors.