Pretty much all my riding is solo, and for all the reasons stated here.

There are only two reasons I can see for riding non-solo. One is to enjoy a social occasion. That's a good reason. But if people separate then it is no longer sociable.

The other reason is to go faster by drafting. But that's like always starting at the top of a hill. Sure you can go faster but it doesn't prove anything. If you aren't racing or trying to catch a train then it's a moot point how fast you go.

I tried a group ride last year, quickly realized there was no group. I understood then that biking is a solo, contemplative activity.