It was my regular route (although not my usual flight) and I normally see somewhere between 40-75% load on the route, with CE load usually poor (rarely above 50%). But if you combine three flights per day into one flight per day, even though an A321 was put on (instead of the usual A320), it wasn't surprising that it was full. I also suspect many passengers do not know about rebooking on other carriers, and this particular flight schedule is not far off the alternative full-service carrier's (there are only two carriers offering direct flight on the route, and one is BA). The alternative full-service carrier is almost invariably more expensive than BA too.

The route is serviced by two others but they are low cost and probably not really competing with BA for passengers.

I would be interested to see how the load is if a particular route had NO cancellation.