> compensated incredibly well for very incredibly poor performance
Sort of. They tend to be compensated well, right up until they're fired. The analogy someone else made to sports coaches is an apt one; if a team loses a few games, the coach doesn't get his pay docked, but if a team loses for a few seasons, chances are he'll just be out of a job.
Plus, in many cases it can be hard to determine whether a CEO's actions led directly to a poor quarter, or if it was just a bad quarter and they handled things appropriately. And if pay was tied directly to financial metrics, there would be an incentive to play the numbers game.
It's important also to remember that the people determining a CEO's salary -- or at least giving it the thumbs-up -- are typically the biggest owners of a company; the CEO's pay comes out of their pockets in greater proportion than it does anyone else's. If they think that their CEO is doing a ten-million-dollar a year job, who is anyone else to argue? If they thought they could get someone to do the same job at half the salary, doubtless they'd do it; I doubt they enjoy spending that much, but they think it's necessary.