Why on Earth am I single?

If anyone gives you a smart*** answer, ignore them. You asked politely and you didn't sound y - you sounded honest and sincere. Understanding all we have to go on is this couple of paragraphs, the thing that stood out at me is that you said you don't go out much. I would guess that is a cause - not an effect. You could go out alone or with friends but your chances of finding someone will be much better if you're out there every now and then! :) Don't go out looking for someone, just go do the things you like to do but also where you can be seen and be social. Something that requires you participate in something with others. A team bike ride for charity, a conference for your job - something along those lines. Skip the bars and clubs - people aren't always themselves when alcohol is around. You sound intelligent and nice enough so it's really just a matter of time. Good luck!