How will ethereum acquire 51% consensus to move to proof of stake?

Please feel free to correct any misunderstandings I have

In order to move from proof of work to proof of stake my understanding is there will need to be a 51% consensus among the network which is currently controlled by miners.

My question would be why would miners agree to move ethereum away from proof of work where they have a vested interest in the millions of $$ in mining equipment they have?