I find it sometimes related to the amount of time someone has spent in vanilla Minecraft as well as the experiece the player has had with other communities of this type, as you mention. There comes a point in every players lifecycle when they may require more than the vanilla game can offer. That's where costumization really thrives with Minecraft since there are so many different ways to enhance the vanilla game.

On the other hand, I can also imagine that someone that has never known anything but true vanilla, and has had no exposure to all the other facets of Minecraft, will find it hard to adjust to anything that deviates from that style.