I think the theme of the article was less that they have nothing more to offer but that the things they offer are rarely followed up on. They become disillusion

I think the theme of the article was less that they have nothing more to offer but that the things they offer are rarely followed up on. They become disillusioned with the ability to get things done. That it's relatively difficult to get promoted into a position of power as much as it is to go to another company and try to get things done there - at the very least you get another throw of the dice with people who might be more inclined to listen to reason.