You can only transfer ONCE in or out of your account per (calender, I think) year. You may make multiple reservations. So, it's more worthwhile for someone to rent to someone than to transfer to someone. Especially if that transfer is for a small number of points.
Also, renters are a much larger target audience for someone who needs to get rid of their points. Only DVC members can do a transfer, you can rent points to anyone.
I've only done transfers in and out of my account when we needed or had extra points. For cash. I'd rather do a transfer with a fellow owner than rent to a non-DVC owner. Once the points are transferred, the other member is out of the picture. No more connection to the points as you still have if it is a rental arrangement.
Another key reason is that banked points cannot be transferred. Often time people bank points when they don't go to WDW in a given year under the assumption they'll go the following year. If something changes and they aren't going to use the points themselves the following year, since they've already banked them they cannot transfer them.
If someone renting points has what you're looking for, ask and see if they're willing to transfer. Many may not say transfer knowing there are far more renters looking for points than DVC members wanting a transfer.