If we didn't have fixed home worlds, they could do a rolling maintenance and take the servers offline one at a time for the hotfix. It's what we do for the duplicate servers of the software that I work on IRL, and it's what some MMOs that utilize AWS or temporary instanced worlds for their server space can do.

However, because the in game worlds for XIV are fixed and persistent on a single server cluster, they don't get that option. It's pull the servers down, apply the patch, run the post patch checks, then put them back online.