Trump says X, traders jump on positions that would benefit from X to try and get out in front. However other than the speculative betting there isn't much movement. Then X doesn't happen, so there is no long term movement. The traders disengage from their positions trying to take as little loss as possible.
This happens over and over and more will learn that acting just loses you money. It's why markets don't do fuck-all in response to Alex Jones. It isn't like his message isn't out there for the world to see, and actually more widely watched than I can fathom, but they don't believe anything will happen based on it so trying to get a first mover advantage can't happen.
You only gain an advantage by getting in first if the move happens. If it doesn't, at best maybe you can get out without a loss but usually you are going to take a hit to some degree. Thus you act only on those things that are likely to generate a move.
Traditionally, things the president said would qualify. However Trump is anything but traditional. He shoots his mouth off all the time, regularly contradicts himself, and changes his mind often.