Syria - the USA has waged a proxy war on them.
Iraq - the USA has waged an unrighteous war on them.
Iran - due to misunderstanding about Iran's Anti-Zionist stance and their involvement in destabilizing the Arab League countries why would you let them go to the US?
Yemen - an extremely unstable country that is the homeland of anti-American terrorists
Libya - the USA put a hit on Qaddafi, what's the chance of revenge attack?
Somalia - the USA did little to stabilise their country - why were they even there in the 90's?
Sudan - the USA did next to nothing to help the Darfur region.
7 countires with plenty of reason to hate the US. Is the point of the ban to 1) appear to keep campaign promises and 2) recognistion that the US has made people from these countries pretty dang angry.