Dragons were derived from wild azhdarchid stock long ago, genetically engineered then tinkered with to optimize their metabolism for racing. Actual azhdarchids were lazy things, capable of flight but mostly hunting on the ground for smaller raptors and their young. In contrast, racing dragons were entirely dependent on human-supplied energy-rich nutrients known as zip fuels, and were bred to go as fast as possible in a straight line without exploding. They weren't particularly intelligent: ideally they reached the finishing line without falling out of the sky from heat stroke, or cannibalizing each other on the wing. While it was possible to watch the dragon races in absentia, the telephoto coverage lacked some of the rewards of the in-person experience: the angry raptorial screeching, the rich aroma of draconic diarrhea, the potential excitement of a third of a ton of racing termagant detonating a hundred meters overhead. So of course the aristocracy thought it the greatest of sports after hunting, shooting, and whoring, and placed their bets accordingly.