I never posted anything about the dynamic being "mysterious", but there is a dynamic. Miners are speculators too, and because common sense tells every miner that higher difficulty = less profit - and therefore an increasing number of miners will be shutting off their ASICs, then other miners could see that as an opportunity.
Plus Bitcoin's price projection.
If as per the topic title, the reward is gone and we see the fees at this level it means the network won't be able to fund 600Exas but 18Exa, so it terms of raw number the amount spent on gear to overpower drops from 12 billion to 360 million! Same for the power requirement!
If we're going back to that debate, then the blockchain should have other uses/different kinds of utility for different kinds of users so that miners will continue to be incentivized to secure the network. But that still doesn't say that there is no dynamic between the mining difficulty, the miners as speculators, the current price of Bitcoin, and it's projected price in the future.