Implying dentists will choose expensive gear, because successful dentists have access to the full price range of gear for most hobbies.

In cycling it is because some dentists buy the most expensive stuff even if they are only riding 20 miles once a week. Some years later they'll sell an originally 10k bike, and it has less than a thousand miles on it. Enough dentists have done it that it is now just a term you call anyone who way overbuys their needs.

My old dentist got into cycling after talking to me about cycling. He ended up buying a 10k+ bike even when i told him not to. He rode that summer but after that the bike stayed mounted in his office. I used to poke fun at him for being the meme