Because I would feel like I were taking advantage of the hotel/resort by unloading my free nights, especially at the most expensive LHW properties. LHW properties do not function like airlines or chain hotels that normally allocate seats/rooms for award reservations. I do not know how the Leaders Club awards work, but there is no way properties are compensated at anything close to their published rates.

On the other hand if I were to stay for seven nights for the price of four (using three free night awards), I would be getting a very good deal, but also giving the hotel/resort a decent amount of business. I am sure a positive ratio of paid nights to award nights would affect the hotel's perception of a guest, and would lead to better room/villa allocation, among other things.

FWIW, when I have redeemed awards at chain hotels (e.g. high-end Hyatt), I tend to combine with paid nights, and to have high incidental spend. I feel that properties take me more seriously as a result.