My thought is that they don't say "no" because they are waiting for their top pick to confirm or deny.

When I did hiring, I had several top candidates take a different position, so I had to go to a second or even third choice.

They don't see that as part of their job. On the short term that behaviour probably doesn't create problems for them. On the long term, they likely will be responding to job adverts themselves :)

Anyway, no answer is sometimes preferable to some of the nonsensical standard doublespeak letters you might receive ("niet weerhouden...").

Respect is far to be found in these HR practices, in my experience. It usually reflects in the business who took them on board. Once you see through all these efforts to make people behave exactly like they want, I doubt there will be much workplaces left considering.