Like the law or not, that's who your nation voted for, and the government has the power to make life very difficult for corporations.
Also, let's be real here. The travel ban doesn't affect these SV companies. How many employees are going to be coming from Syria, Iran or Yemen?. Are the positive optics worth the difficulties? The public is already weary of corporations becoming too powerful, this will only feed into that distrust, and possibly alienate ~50% of the population.
Political statements in either direction are almost always a losing proposition for corporations.