There are two separate entities involved in (virtually) every hotel stay. One is the hotel group (Marriott, Hilton, etc) and the other is the hotel. With the rare exception of corporate-owned hotels, these are two separate businesses.
The hotel group run the frequent guest program. They set the policies regarding the redemption of points. If you're questioning the purpose of certain policy, you should think about the motives/goals of the hotel group...not any individual hotel.
Personally, I can't provide an insider take on why that policy is in place. I did once work in the central reservations office of a hotel group. But, it was one that did not have a formal frequent guest program. Had I worked for Marriott or Hilton, I might have actually asked because it is a bit strange.
I did, however, work in several different hotels over the years. Two of those jobs included working as a Revenue Manager. From that perspective, we would have gladly accepted points instead of cash for a no-show if that had been an option. Points are a guaranteed reimburse. A cash no-show charge is not.
Side note:
Many FlyerTalkers assume that hotels love no-shows because they get money without having to provide the room. But the reality is that many guests will dispute the charge. One of my hotel jobs was in Accounting. I had to respond to all chargebacks. We almost always lost no-show chargebacks. All the guest had to do was saw they canceled (usually that was a lie) and prove they were at another hotel or in a different city. The credit card company almost always sided with the guest in a no-show dispute. Every hotel will be different. But, I'd guess we only collected money on 30-40% of our no-shows.
In the end, without access to proprietary information or some former insider willing to talk, I doubt you'll find a good explanation.