Because for most people wanting a relationship isn't something which causes them a lot of angst, it's just something they want and are willing to work for without it being an obsession or object of misery.
...You've missed the point. The point is to do things without constantly worrying over whether it will lead to a relationship, but instead to find value and enjoyment in your life without a relationship.
That said, it certainly will increase your chances of finding a girlfriend in the long term, there is nothing more boring and off putting than someone who constantly angst's over not having a relationship, or puts all their hopes for fulfillment and happiness on a theoretical other person and the opportunity to put their dick in them. As you are now what do you actually have to offer to a woman?
