Why is no one single anymore?

Why dont men and women actually be single, alone, unattached, for a while before they start pursuing another person? Why is everyone always attached, and that makes it difficult to actually meet someone who doesn't already have a gf/bf. Everyone you meet might flirt and seem interested, then you ask them, and they tell you they have a gf/bf. How can you expect to meet anyone when everyone is already with someone else? You have to take time to enjoy life alone, before you pair up with a new person, or to get over the last relationship.