This is where common sense kicks in. Turbine makes the rules. Large guilds provide service to large numbers of Turbine customers. Turbine rewards large guilds with easier advancement.
It's how they get the small number of players that are able to do what it takes to run guilds that help keep their least invested customers here to be willing to go the extra mile to do so. Keeping a small guild of DDO fanatics happy just isn't doing as much for the people who hand out the rewards, so how are they justifying they deserve any sort of bonus for doing so?