To create incremental patch updates requires much more organization, not that I'm saying the devs are lazy or anything. If you make 1 change to an event, that's 1 map that you have to put into the patch. If you make a change to an event on a different map, that's another map you add to the patched files. This all sounds easy, because it generally is, if you have good organizational skills. If you edit 1 map, but forget which one it is (or forget that you even edited it) it could cause a chain reaction of bugs that could take a lot of troubleshooting to find. In a situation like that, it'd be faster to just release the consolidated, working master files (which is how it currently is.)
This game has a lot of maps. As far as RPGM games go, this one is pretty big. The amount of maps is just one aspect to look at though. Some of the maps are VERY cluttered, because there's a lot of stuff that could happen in them. Just look at the second floor of MC's house. That map is littered with events because of all the branching stories. If you were to make changes to that map and not have it documented properly for future reference, you could be dealing with a lot of game breaking bugs, because that's pretty much a hub map.