Presumably because they believe keeping Musk will increase value long term, so they are still maximizing the value of the future cashflows discounted to the present.

The size of Musk's ownership stake adds another layer to this metric, but at the limit, that really that just means the words "they" in my previous statement can be replaced with "Elon Musk"

No, the reason most voters gave is that the payment was promised, not that it maximized their returns. There are any number of projects that Tesla could spend $50 billion on that would provide a greater return to investors than giving it to Musk. Even giving him a fraction of that would have been enough to retain Musk over giving him nothing, if they really believe Musk's leadership will be positive for future returns.

I suspect many Tesla shareholder believe they are investing in Musk, rather than just Tesla. That explains much of their behavior.