Maybe what the buyer wants isn't readily available in the resale marketplace and the buyer wants points NOW! Smaller contracts in a specific use year can be tough to find, and the additional cost may not be that much of an incentive (Over the life of the contract, annual fees will outstrip the initial purchase price). Buyers need to balance the initial cost with the other factors that are important to them.
Disney can break up a larger contract, but they have to be willing to buy one through ROFR. It is likely that someone wanting to buy a small contract will sit on the waiting list for a while, so the "I WANT IT NOW" argument doesn't hold water. But, for a specific, small contract, direct might be a little bit quicker than waiting for the right contract to come along.