Actually, quite a few Apple Watches have sold on eBay at high prices.
How many is "quite a few"? I just did a check of the listed auctions and there are fewer than 1500 Apple Watches currently being offered. You have to filter out the junk to get an accurate count. That does not translate to "quite a few" when millions have been sold worldwide. Even if three times the current listings were sold, that's a drop in the bucket.