Sounds like I'm in the minority, but I find I play better/concentrate more when I'm alone. When I play with others I tend to feel rushed, like they're waiting for me to play so they can hit or something. When I'm alone, I take more time to line up the shot and my practice swing(s) are more deliberate and with better tempo. It's my own fault for not taking ownership of my own game, but it's a big reason why I perfer to play alone.
I will say for myself also, that I'm not someone who will come out at 9am on a nice day and expect to be let on the course by myself, especially because I walk most of the time. I'm almost always first on the course, OR I will come later in the afternoon when it's slower, at least on the tee sheet. I may run up on some people, but unless I'm chasing the setting sun, I'll be walking and taking my time so as not to play behind people.