For it to be a federal crime there (typically) needs to be an inter-state aspect to it. It's typically very easy to show that the communication crossed state lines if it was over the Internet, which removes jurisdictional challenges.

If you defraud your local grocery store with your coordination meetings in a local mcdonalds, it's _probably_ a state crime. ()

() (1) there are many ways a crime can slip into federal jurisdiction; (2) IANAL, so don't take advice from me when you're about to commit fraud.