I am single because no one is interested in me, and I am interested in no one around here. I tried online dating, once, and it didn't go well. Perhaps I shouldn't swear off online dating sites because of that one instance, but it definitely made me want to take a break from it.
Other than that, I don't know the whys. If I try to think of them, I usually end up being negative towards myself, which isn't good. So, I don't try to question why things have or have not happened in my life. I will continue to grow as a person in this season of singleness, and I think that's the main important thing about being single: Grow and learn (about yourself and God) no matter what your circumstances. Have fun. Do things. Don't let your relationship status determine your happiness. Relationships certainly can add to one's life, but they don't fix everything.
Despite the above, I'm not saddened or distraught. I'm only 23. That's just the way it is right now and I'm okay being single. *Shrugs*