If Disney cared, they couldn't eliminate renting, but they could make it far less attractive. For instance, renters do not get access to meal plans or magical express. Members get priority check in - if you are not staying in your own room on your own points - or traveling WITH a member staying with their points - you will get what is left. Over time Disney could figure out which rooms get the most complaints on them (they might have that data now) - bad views, too far down the hall, too noisy - and hand those out last - to those waiting renters. Disney offers perks to anyone staying on property, but those perks do not need to be extended to renters (or frankly DVC at all), so they could (and given coding of magic bands for perks - it wouldn't be too difficult) limit early entry for instance for non members staying on points not traveling with a member.
This would mean that when you gift your points to your adult children, they wouldn't be traveling with you and would lose some of the perks, but Disney COULD do this if it were important enough to limit renting. While some members would find that problematic, I suspect as many or more would be thrilled by priority room allocation for members - knowing that if someone isn't getting into their room until 7pm to discover its the room over the luggage loading area for Magical Express or the HA room they don't need or the weird room with no balcony - it probably isn't going to be them. And I don't think it would make sales less attractive, since renters would know that with membership comes advantages in check in.
That they never have done any of this makes me believe that they would rather have occupied rooms than discourage renting.