This --- There are more contracts in existence than 10 or 20 years ago, so of course there are more resale contracts.
Secondly, as contracts (and owners) age, there may be an increasing percentage of owners looking to re-sell. Not many people are going to re-sell 3 years after buying. (some will, but not many). On the other hand, after 20 or 30 years... Kids all grown up.. owners getting too old to travel... owners passing on, and the kids not interested in keeping the contract.
It's also important to remember that Disney can tightly control the direct supply of points for sale. Stop building new DVCs... declare fewer rooms and use them as cash rooms... So Disney can prevent the supply of direct points of getting too high. In contrast, resale is always growing in supply, not necessarily with an increase in demand. .