Accepting sidecar outfits are very rare indeed, mobile or otherwise, so seeing them out on the road is extremely unusual.
Other than specific sidecar events, especially our sidecar club activities, seeing them occurs for us almost as often as birthdays.
On the other hand it's then surprising how many times sidecars crop up for sale locally on such as Fleebay. Seems there's quite a few in sheds, garages, back yards, and permanent hibernation. Not great numbers of course, but certainly more than those in action.