Because some people will realize that they have more time than they thought and switch to a longer path or realize they had less time and switch to a shorter path or realize that the prompts on another path fit better where their fanwork is heading. I myself like one of the alternate ways; I'm doing the purple > red > yellow because it fits my idea the best. (I would have otherwise done the short fanworks path.)

The rules, in a nutshell, are: pick a path, create new material for the prompts (aka already-created material does not count for the prompts), and reach the center on or by March 31. Everything is a self-challenge so you don't need to concern yourself with how others are moving around the board. I do admit I am having a very hard time understanding how they're not obvious. If you're confused I guarantee others are as well and I'd like to fix that as best as I am able.