Let me guess: You have never owned a station before. Believe me, it shows.
Nope. I'm simply looking at this from the paradigm of value creation and the value proposition - that is the question of where the value resides. From the discussion beginning it was established that users migrated from AM to FM because of the giant order of magnitude gained in FM quality. Thus, to the end user, FM inherently possessed more innate value as opposed to the alternative medium, AM - the value of FM versus AM was recognized by listener migration (also more generically called a change in user behavior).
Unlike FM versus AM and broadcasters' historical experience with listener migration from a lower to higher value medium, HD-1 versus FM analog DOES NOT possess any value add - the listener doesn't see the value of HD-1 because it is scant compared to FM analog.
So, hypothetically speaking, blue sky thinking, broadcast licensee's have only one option to induce listeners to migrate to HD-1 (and thus HD's>1), is to impair the quality of FM analog. Turning off FM analog would be the extreme case, and neither the muddying FM option or complete shutdown is viable in the real world of revenue generation.
The mere fact that listeners don't / won't migrate from FM to HD-1 is a case study in itself of the failure of HD Radio due to the lack of value added by HD Radio.
You didn't take me at biblical-literal did you?
Particularly since not only is this hypothetical FM to HD motivation suggestion completely ridiculous, but also my claim that loudness and distortion lasting more than hours is an actual medical emergency is a highly moronic, dim whited thought at best, intended as entertainment only.
Please don't attempt this at home!
HD is an answer to a question that was never asked in the first place.
If you look back at the pre FCC deregulation days circa 1989, there was a legitimate need for HD Radio.
(1) The state of FM audio quality was significantly impaired as compared to the CD medium due to the state of development of analog Audio Processing and broad use of magnetic tape, cart machines, etc.
[the mitigation of inferior FM audio via DSP based, multiband audio processing and hard drive based audio filled the very perceptual gap between FM and CD]
(2) When the ownership rules limited a broadcast licensee only (2) stations per market, one AM and one FM, broadcasters would have been overjoyed to have the full three channel FM capability, as it would have automatically expanded a licensee's revenue stream from 1 to 3.
From this point, developing HD-2 / HD-3 as a real alternative to competitors would have been attractive; competition between single FM licensee's would have been driven actively in pursuit of listeners and thus revenue.
[When you can own 3 or more analog FM signals in any give market, a broadcaster no longer needs to develop HD's>1 to add revenue streams; the market is saturated and it's overkill. Thus, HD subchannels loose their value in the deregulated marketplace of multiple ownership. Thank the FCC and deregulation for hampering the value of FM multicasting]