The answer to those questions would be very long and include many causes. To add a speck of light to the confusion generally seen from news organizations, some market indexes include manufacturing based in the U.S. but with actual production happening overseas. Other reports come from surveys of manufacturing on U.S. soil.
Wall Street is loaded with import interests, and a large portion of investors derive their incomes from the various levels of government in bed with foreign national interests—mostly anti-Trump interests.
ISM: U.S. Manufacturing Growth To Continue Throughout 2018
https://www.inddist.com/news/2018/05/ism-us-manufacturing-growth-continue-throughout-2018