The reason they don't allow custom uploads to have hats on them is because it would basically be a custom hat upload as well. Staff can upload their own hats anyway, so it doesn't really matter if it's on their head.

Anyway, the rules make sense... They don't want small heads because it looks inconsistent with the rest of the graphics on this server. They don't want transparent heads because they are hard to see. They don't want heads that infringe copyright for obvious reasons... They don't want glasses because they are sold as hats. Regardless of the number of rules, there's plenty of character customization you can do within them.