99% of my rides are solo because most of my rides start from home and I have all the hills I need within 20 miles. It is just easier. My former riding partner got sick of my competitiveness and quit riding with me. Note: he was kicking my ass in the beginning but that changed over time as I learned how to climb.
I plan on participating in a couple gran fondos this year but that is more to get exposed to some areas I have yet to ride and less about being in around other riders.