If they invest elsewhere, they will have limited access to the U.S. market—that is Trump’s policy it seems.
If the U.S. has one thing going for it, it’s the strength of its market, characterized by high consumer spending and strong potential for growth. Contrast this with the Japanese consumer market, for instance: in real terms, salaries have not increased over the past 10 years, and consumer spending is below what it was a decade ago. (Note: I love Japan, but this is the reality.) European market is between these extremes I believe. The U.S. market may be significantly more attractive to most companies.