The US Market is definitely more optimized more than say European, at the sacrifice of the common good of the people and to the advancement of broligarchs. Trump is doing is best to kill even that (I think it's not his intention, he's just not good with money), via tariffs and crazy economic policies and promoting even bigger deficits than we had during covid. I'm not sure how much longer it can fly high though.
Economic instability and uncertainty. How high it is compared to other markets is debatable it has increased significantly this year due obvious reasons, though