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