The Americans have significant interests in these seven countries - financial interests, and more importantly, security, military, and anti-terrorism operations.  If these seven countries do the same thing, impose a travel ban or even kick the Americans out of their countries, the US would be significantly compromised and vulnerable to.....terrorist attacks, maybe?  I'm not an international expert, but it seems American interests, American intelligence, and many individual Americans, have a lot more to potentially lose with very serious consequences.