Board Thread:Suggestions forum/@comment-33763020-20180111104851/@comment-26410366-20180111204655

It's because of how Minecraft works. The world loads 16 by 16 chunks of land at a time, and only things inside those chunks are able to do anything. As far as the server knows, they almost don't exist. That means that the gold banner is about as big as it can be before problems start happening. It wouldn't need to load all 64 chunks, just the one the banner is in. Still not ideal if you're on a server that's been around for a while with a lot of large builds protected like this.