At some point the price will fall to a level where the early miners are no longer willing to sell.

Where do you think that point might be? The Steem price is already well below the lows from early May and late June/early July. Market cap is around $25 million, down from the near $400 million peak. There doesn't appear to be any slowing of the downward momentum.

If most of the large stakeholders are still selling into that, then what would make us believe that they wouldn't just keep selling whatever they have left, despite the price continuing to crash? The return on the initial "investment" has probably been more than sufficient to not really care if they're getting a few hundred dollars per week or a few thousand per week at this point. Those who are witnesses and are actively curating (which is becoming more automated) on the platform aren't even really seeing their stake decrease. So powering down and selling, even if they're only getting $200 for it, is still likely a weekly profit for them. The price could drop to a penny and they would still get hundreds of dollars per week.