Many watches get resold because they were:
- a choice that seemed a good idea at the time but ended up not getting used much,
- an unsatisfying attempt to skimp buy buying something less than what you really wanted,
- a fit to the fashion or tastes of a different time,
- no longer a fit to the owner's needs, such as a very dressy watch owned by someone who's company has gone to blue jeans casual dress code,
- chosen by an indecisive buyer that later regretted the choice,
- a bad financial choice sold to try to get some of the money back,
- or one too many in an large collection.
Particularly when you have multiple watches (how many people here have 5 or more "good" watches?), you may find that some end up not being used much.
In addition, the change in many corporate dress codes from business suits down to casual or even blue-jeans has changed many people's needs. My business wardrobe used to be seven business suits, 14 ties and one nice watch. Now it is zero suits, zero ties and multiple nice watches.