Because I like the aesthetic. There is only one canon depiction of an Ansei that I know of (Frandar Hunding) and the armor he wears looks more similar to the Ancient Falmer set than arguably any other set. asgard suggested using glass armor as an alternative, which was also one of the sets I was considering. If you don't like the Ancient Falmer set, or don't have Dawnguard, try Glass instead.
Because I like the aesthetic. There is only one canon depiction of an Ansei that I know of (Frandar Hunding) and the armor he wears looks more similar to the Ancient Falmer set than arguably any other set. asgard suggested using glass armor as an alternative, which was also one of the sets I was considering. If you don't like the Ancient Falmer set, or don't have Dawnguard, try Glass instead.