Why else are these busy academics at your viva?
They have their own research, their own researchers, teaching, marking, admin, responsibilities and a life.
They’re not paid vast sums of money to be an examiner. They’re not simply a friend of your supervisor doing a favour.
It might be expected professionally to take on the role of examiner sometimes; they don’t have to do it for you and your viva.
They don’t have to be there. They get to be there.
They want to be there.