I suppose it is because:

1) I almost always ride with a group
2) I ride to have fun
3) I have been an Engineer/mechanic all my professional life

that I have no desire to work on a bike on the side of the road with tools that will fit in my jersey/seat bag on a Saturday or Sunday, except for fixing a flat. Besides, I would not consider holding up the group long enough to do anything else. I consider it bad form to repair a flat instead of changing the tube on a group ride.

Could I fix most things if I had to? Probably. Would I attempt it? Doubtful.

I make sure the bike is ready to go in the parking lot. If the unexpected happens, it is either the wife, one of the kids, or someone in the group that will come and get me (That actually happened last summer to a group member - he sat on the side of the road with a split rim until the group got back and then someone went and picked him up.)