Because Trump went to election on "a total and complete shutdown of Muslims entering the United States" [0, donaldjtrump.com]
The fact that it was implemented as a ban on citizens from the most prominent Muslim-majority countries (as seen by the eyes of the average American voter, who forgot about Saudi Arabia) could be interpreted as a way for Trump to say he kept his pledge while not being instantly impeached for not protecting the Constitution as is the job of the president
The fact that it was implemented as a ban on citizens from the most prominent Muslim-majority countries (as seen by the eyes of the average American voter, who forgot about Saudi Arabia) could be interpreted as a way for Trump to say he kept his pledge while not being instantly impeached for not protecting the Constitution as is the job of the president
[0] https://web.archive.org/web/20170130001335/https://www.donal...