Because people aren't actually like that in real life. Just because they've gotten a to a particular lifetime job in life, it doesn't mean they don't still crave the approval of their peers. They don't live in a vacuum. They want to still be invited to speak at the places they usually speak, attend the same parties they usually attend, etc.
And beyond that, there's a more fundamental issue: people like this are chosen for these roles because of their fervent, polarized political beliefs. Their principles, if they have any, are either aligned with or overcome by the politics. Their willingness to listen to reason and step outside their bubble is limited, unless doing so lines up with their politics.
