The seller is not the same as the eBay member listing it - the eBay member is a broker. It is not in his best interest for this to end up as a rental, because then he doesn't get his fee/commission.
The "comparable" unit obviously isn't comparable - it is a RTU that ends in 2027, per the resort website. That sells for $16000 on their website, but again, has 19 years remaining, not just 1.
Obviously it would make more sense for the "seller" to simply rent the unit out, and not pay any fees. That does entail a small amount of risk, but why pay closing fees and transfer fees when they're not necessary?
It might be different if the current owner has an option to extend the RTU at a substantial savings over the current prices, but otherwise it just doesn't make sense.