OK, I'll go one further. Watching a bunch of people do barrel roll after barrel roll, and backflip after backflip in the surf also gets dull to watch. That doesn't mean they're not fun to do, or hard to do, but they get old quickly from a spectator point of view. Variations are cool no doubt, and watching something new is exciting as hell. But watching people so the same thing over and over? If you watched FMX and every came out and did the same trick, that would be dull too - however impressive the trick.
Our brains are designed to react to changes, and to tune out things that don't change (the way we tune out a constant background noise, or don't even notice the pile of dirty clothes if we walk past it often enough). Variety is what keeps humans interested, and 10 flips in a row is the very opposite of variety.
That's why the rodeo was so memorable at Nationals - one guy did it, and nobody had seen anyone do that in competition for a while. It was way more memorable than all the backwater backflips. Is a backflip harder? Debatable. Are they more fun to do? Maybe, but not according to Jeff's face. Is a rodeo more fun to watch? Yes, against a backdrop of all backflips, in the same way that a backflip is (and was) more fun to watch against a backdrop of rodeos.
Variety wins.