They are sucking the little guys in and when they are ready they will pull their money and crash the system. They will then buy everything on the cheap!
The stock market is based on what corporate stock is worth to buyers on any given day. What stock is worth depends on corporate profit. Corporate profit these days comes mainly from overseas — meaning it is not dependent upon the U.S. economy at all.
So the reason the U.S. markets sometimes shrug off what is happening in the U.S. economy is that what is happening in the U.S. economy is only a tiny piece of the puzzle as to how corporations make money and how much they make.