Long thin wire has resistance obviously. For arguments sake, if a company used small gauge wire they would need 50 feet of it in order to get a resistance of 4 ohms. If they use a bigger gauge wire, they might need 150 feet now in order to get a resistance of 4 ohms.
Like most things in audio, everything has a trade off. More coil means more surface area to dissapate heat, but also reduced efficiency because now it weighs more.
I'm sure there's a lot more to it, but that's my basic understanding of it.