It s a very unique question because many people are single due to their work they are not interested in all this type of things and some people are single due to does not have a good looking face and rejected by every girl.
In india many people are single due to family reason like 
1)Poverty 
2)single because of family problems
3)single due to attitude
4)Not interested in marriage

All people have different mindset and they are having their own opinion for this question but the general people if they are single are listed and i think this is the exact reason for single person.