Lots of people don't have connections to suitable forums to sell watches, and avoid Ebay.
They see local dealers and the national ones as being a hassle-free method of selling their watch that they have either bought speculatively, or simply want to move on.
Many simply won't even seek out likely local dealers - preferring to do the deal by internet/e-mail to the likes of Watchtrader or whatever they are called.
My local dealer, who sells quite a lot of almost new Rolex - said "I give a fair price and it is hassle-free for them".