He paid $50M to exercise $100M of options, but didn't sell them.

Why did he do this? What are the advantages compared to holding on to the options until ready to sell?

I can think of one: to qualify for the lower capital gains tax rate if he waits a couple years to sell. (I'm guessing that most of that $50M is the Alternative Minimum Tax, which makes me wonder, would be refunded some of that in the capital gains scenario?)

But methinks there might be another reason. Were those options expiring? Does exercising them give him more control in the company? Is it simply a statement of confidence?