Don't all of these schemes remove (waste) one night from the available inventory for award rooms that someone else might need? Or the hotel might sell to a paying customer?

And to what gain? OP gets another night's stay credit?

I am actually amazed that Hilton credits award stay nights for elite qualification.

Usually, when we lose a benefit, it is because the hotel or airline claims that the benefit is being abused.

What the OP suggests sounds like abuse.