The key signature allows the composer to use less accidentals which makes the music less cluttered. Just like the other person who answered this said when a score with multiple instruments is written it is almost always all in the same key to keep the music organized (their answer is better)
I believe we didn’t accept abstract as art for so long because it was different. When things are different we often (as humans) avoid it or think less of it. In this case it’s art. People often think there is a handbook to creating art. But there isn’t which is why abstract art was not accepted. You had to develop a story for it instead of it developing a story for you.
Hope this helped!!
