Someone fear something when it is out of his or her control, people by nature like to control everything in their life. If they are unable to do so they would be scared of it. The same thing applies to marriage, it requires to quit your own way and submit to a common good, it requires to deny yourself. So we mostly refer our parents when we think to marry, how were my parents acting before their children? how did they deal their challenges?. Mostly young people who grew up in loving and caring parents would like to marry soon. On the other side young people who grew up in a fighting, quarreling, divorced, separated parents abstain from getting married or it would be hard for them to marry. I think it is parental influence for young people for the fear we are talking about.
Marriage is something beautiful and wonderful when you have it with the right person. But some people fear the commitment will cause them to be unable to do the things they want to do...I have to say,it seems MOST of the reasons people fear marriage is because they are not with the right person,or because they aren't trusting God to help them...for "..perfect love casts out fear..." God wants the best for us,and if we trust Him,He'll bring it to us in His own good time.