Why does Daredevil no longer wear the better season two costume in season 3, but the black, unarmored costume from season one?

Marvel's Daredevil on Netflix

Here it is explained by DD actor Charlie Cox:

http://collider.com/charlie-cox-daredevil-season-3-interview/

The content of the costume change in the series is not discussed. They wanted to set a sign in season 2 with the red costume (which leads to a conversation between Matt and Father Lantom) and has decided to take the black again for season 3, which by the way is not completely identical to that in S1.

With the dark costume you wanted to underline the dark tone of the third season, and Cox was happy about wearing the more comfortable costume again:-).