I ride solo mainly because of my work schedule...swing shifts really suck...
Also there are not a lot of riders in my area so even seeing another rider is a surprise.
I prefer riding solo...my schedule, pace, distance, area...no compromise.
I do enjoy group riding now and then but it seldom works out as good as I hope...pace is too fast, slow...people not knowing general group riding etiquette...etc.
I do miss the team I rode with and the training rides. I also miss racing a great deal but again with my work schedule and living in the hinterlands it is a long drive to a race when you can find one.