It's just the opposite. Everyday life is becoming more violent. With 24/7 media, the internet, etc., the average person is inundated with more violence, more death, more destruction than ever before. It's literally everywhere. Compare that to the 1960s when the most violent thing anybody ever saw was Rowdy Yates shooting somebody on Rawhide.
It makes sense that people of yesteryear turned to sports to get their 'violence fix'. That isn't needed in todays atmosphere. Just the opposite. Sports is entertainment, an escape from everyday life. As such, people are turning away from violence (fighting) in sports.