Re: his work there is done
Because they know very well how to sell themselves, to people who have the power but not the brain to make the right choice.
In a ISV company I worked for years ago, one day they bought another one, which was in some troubles. We believed they bought it to acquire its customers, maybe a product or two, and expand the company.
With our big surprise, the owner of that company was made head of all development activities, and is vice (one of the worst person I ever met, as I was going to discover later, always ready to stab someone in the back as soon as it could), the technical head.
They didn't take much to put in troubles the company again, with a string of bad decision while making skilled people go away - eventually the company went bankrupt (among other stupid decisions).
At least one of them is no longer in IT, now he's in the "art market" - probablly selling fakes or the like. But this too tells a lot of how some people are very good at selling themselves for roles they can't really fill.