My main village had hundreds of different villagers, particularly librarians with useful enchantments. They have all been replaced with leatherworkers. Hundreds of leatherworkers. Not useful. Same thing happened in any other village that was created from rescuing zombie villagers. All of those villages have been reduced to one single type of villager. Again hundreds of one type. Maybe that was the first villager rescued that founded the village? The villages that were built up from existing villages have a variety of villagers.