They have to recover that cost. Less than 5-percent of the people they bring in actually purchase anything. Same reason as stated above. You are not paying your buyer to come and look at the property. You don't have that cost.
Interval property is a little like a car.
It costs more to buy it new. Then, it depreciates for a while. Unlike a car, after the initial depreciation, an Interval property's resale value usually steadies, then begins to rise. If you paid that overhead cost in the purchase, it will take a while to go through that phase and reach a resale value equal to what you paid. If you bought a resale, congratulations, you avoided that overhead cost.