Somebody does something (an act of terrorism). Instead of fixing the issue at its core, a politician will, instead, do something that is completely unrelated, random and inefficient but that looks like he is doing real work (banning muslims from entry).
A terrorist going on a killing spree is not different than a destabilized white American 30-something going on a killing spree. Both are destabilized (mentally) but for different reasons.
Most people would not care because it doesn't affect their bottom line. Banning muslims isn't an issue for your average American family, even if it doesn't stop terrorism.