The offer that was posted is 40 a night. And if room is 40$ there isn't really any point earnings
If the room is $40 a night then he still gets $8 worth of points back, effectively creating a $32/night mattress run. Not optimal, but there are people on Flyertalk spending more per night for their mattress runs.
With that being said, I don't think most travelers are booking $40/night rooms. I've had a number of people reach out to me, and every single one was looking for a $150+/night resort.