The guild member limit is a limit on full members, Aspirants don't count toward this number. It is in place to ensure that the larger a guild gets, the more costs it incurs (as it should be netting more gold anyway). This prevents a realm from founding a guild and using it as a bank or message group on the cheap. If you want a whole realm to have access to such a thing, then you need to construct more guild houses. More and bigger guild houses create more room for more full members.
