Many are scared of marriage because it is literally a 50/50 chance gamble that it will work. And if it doesn't work out then the outcome is usually devastating- financially, emotionally, and for kids if you have them.
People are waiting to get married at an older age and there are more second, third, etc marriages than ever, but this doesn't cut down the risk of getting divorce.
I think the divorce rate is high because Americans are narcissistic and spoiled. We don't like something, we move on to something better, we upgrade EVERYTHING in our lives. There isn't a general respect for the institution of marriage either. It is not scared like in many countries rather a joke most of the time.