I think there are two different things at work in your argument and in my research, which admittedly, is based solely on reading people on this and other threads. People were lamenting DAH because they did not want to pay for those late-night, sparsely attended hours they had experienced in the past. When we've gone for late hours, my wife and daughter have done it while I've stayed home with the younger twins, so I've no first-hand experience. So it seemed to me that people were saying these late-night hours were a benefit to them because the crowds had dissipated in the aftermath of Wishes.
So that led me to the conclusion that there is :a) a market for late-night hours at MK and b) it's not a huge market. I think both of them can exist without difficulty, because WDW can satisfy that small market with a price, but the market isn't big enough to justify offering them for free (i.e., the late-night experience is not considered by most to be internal to the WDW experience. Disney would have a tough time getting rid of parades or fireworks, because they are considered to be a part of the experience, but late nights are not, or else they would be more highly attended). And I think they could reduce those hours -- which are not stated anywhere on any Disney information -- without significant backlash. Some, sure, but limited, and not enough to deter people from going.
However, DAH throws two other factors into the mix. The first is the limited availability. Disney can't assure small crowds with basic late-night hours -- it very well may end up that way, but Disney could have a night where everyone in the park decided to stay until midnight and there'd be nothing they could do about it. You can't market a hypothetical that has the possibility of not playing out as you describe. However, DAH can easily market reduced crowds and lines, because they control the number of tickets sold. That would be a giant benefit for people to be able to plan a night at MK and be assured the crowds and lines will be small. Just doing that aggressively would increase the desirability of the event.
And the second is that people are paying for it. It's easy to skip late nights because they are an addition to your stay -- for lack of a better term, a gift Disney throws your way. It's just as easy to not go, or to say you're only going to go if you're not too tired or whatever. DAH requires (yet another) plan and commitment on the consumer's part, so attending it would be a priority instead of an afterthought.
The other thing that I may be wrong about (though I don't think I am) is the actual cost to Disney for this is relatively low. All of the hard costs are already in place, so they are talking about marginal electricity and water increases and labor costs. But since most of the CMs would be hourly, and they wouldn't need as many of them, the labor cost would be small. I think it breaks even at about 300 attendees. But without revenue, the only thing it can do is lose money, and that's what I think they'd be trying to avoid.