I think most people don't have the space to retain good birds , if you have race birds that are to be retired to the stock loft after there racing days are over its a one in one out system , so its better to get rid of the older ones esspecialy if you have enough ybs or performing old birds from that bird , some are small back garden fanciers and have limited space , whilst others will have allotments with as much room as they want with no bird limits to how many they house.