Might because of legal issues, the 7 countries that the Obama administration listed as part of the visa waiver program changes and terrorism travel prevention act had already passed through the courts legally.
Maybe it was easier for Trump to broaden this act to a 6 month ban, rather than add more countries to the list because it may have needed more time to get it passed through legally.
He doesn't have any investments in Pakistan or Afghanistan apparently, and this is what the Saudi's said of Trump after his inauguration -
“We are very optimistic about the Trump Administration,” Saudi Arabia’s Foreign Minister Adel al-Jubeir told Al Arabiya after Mr Trump’s inauguration.
“The positions that President Trump has articulated are ones that we are completely in accordance with,” Mr Jubeir said. “Restoring America’s presence in the world is something we – and all of the American – welcome because the lack of an American engagement leads to a vacuum.”