Because of greed. For most humans, what you have is never enough.
A few years ago, Netflix had a reputation of paying very well to lower level senior employees (think L5 and L6), but not as competitively for higher level employees (L7+).
Because even the salary/bonus of a VP at Netflix is never really enough for some folks. And, as sibling comment eludes to, there's always one more ladder rung above you. No, of course you don't get it. Yes, of course you'd live just fine on that salary with tons of money left over. So would I...until I become a VP at Netflix.
But it's the bigger question of whether a person of such morals has VP material written all over them, or if the position causes one's formerly-solid morals to slip a bit (or a lot).