Good question.
I guess the important thing is timing. Since in Ethereum GPU mining is used, there are probably still quite a lot of hobby-miners out there. Instead Bitcoin mining shifted from home-mining to highly specialized ASIC-mining already a while ago.
I assume quite a lot of these hobby-miners are yet serious stakeholders who would love to have a gaming-pc for gaming again.
Professional pools could also profit if there is a good altcoin using gpu-mining. Then they could do PoS in ethereum and PoW on the alt-chain.
In that case the switch would be a win-win for most parties. Yet it needs the given conditions imho.
RE: How does Ethereum plan to switch to POS when miners make the decision?