"Mysterious" here means "via an otherwise unexplained-in-a-single-world mechanism."
There's no mysterious quantum motion for the same reason there's no mysterious energetic motion - because energy / mass / quantum amplitude has to come from somewhere to go somewhere, it requires an interaction to happen. An interaction like electromagnetism, or the strong force. You know, those ubiquitous, important, but extremely well-studied and only-somewhat-mysterious things. And once you study this thing and make it part of what you call "energy," what would otherwise be a mysterious appearance of energy just becomes "oh, the energy...
This is a thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. The previous thread is at close to 500 comments.