people who like expensive watches (ie other rich people) can tell that his is expensive, so he's part of the ingroup. it's an impractical amount of money to spend, even at his steep discount, on something that is also functionally outmoded for most people by smartphones, and thus acts as a high-cost (honest) social signal.

some people also like sophisticated physical mechanics (likely including GP, since he can repair watches), but i believe that's typically secondary.