All that matters is the market's valuation of the currency: it would be irrational for miners to do anything except expand until their costs nearly match the reward.
I think the answer to what you actually said is; miners don't control consensus on the network - it's not up to them, it's up to fullnodes/users who can change the ruleset whenever they want.
And I agree to a point, but miners are the ones that effectively run the network, and there aren't actually all that "many" of them. Without the existing miners willing to contribute the existing network would fall apart. PoS is an interesting situation because it technically makes the miners unnecessary, but obviously the miners are going to say "no" and just keep going with the existing Bitcoin. It would just create another Bitcoin Cash situation effectively, which is a lot less appealing than if everybody switched to PoS and left nobody using the old version.
I think there's a conflict of interest issue here that would prevent such a move even if it would be worth it - the miners clearly have an incentive to keep the current PoW mechanism, as without it they're left holding a bunch of expensive useless tech. And without the miners willing to go along with a move from PoW to PoS, at best you're going to get a split between the PoW and PoS chains rather than a clean shift from one to the other and just create a mess, which isn't ideal for anyone.