I'm a loner by nature. I enjoy quiet, time in my own head, being on my own schedule. I'm a manager at work - people people people all day, I have a house full of kids and dogs... the bike gives me a chance to check out and think...
I get off work at 3:00 and hit the trail on the way home, then go home and have dinner with the family. The local group rides typically don't start until after I am finished my ride... right in the peak of rush hour, and I wouldn't get home until after 8:00 at night.
And I like to pick and choose when/where I ride. I only ride the roads when traffic is minimal. Very early weekend mornings, or pre rush hour. The group rides hit the local roads smack in the middle of rush hour.
And finding the group with the right pace is difficult. Our B groups are no drop rides, and many times C riders show up and the pace drops to a crawl. Our A group has a listed speed range - but no limit. We will get 300+w monsters show up and flat blow the paceline up.