I think this suffices as a summary, "The other reality is the frustration and drudgery of operating in a world of corporate politics, bureaucracy, envy and greed— a world so depressing, that many people quit in frustration, never to come back."

Some of us just aren't cut out to work in a big corporate environment. From what I've seen, large technical companies are made up of two sets, the technical set and the manager/business set. Unfortunately, it seems that the manager set yields a disproportionate amount of influence and power and therefore is "valued" more. I'm sure there are smaller companies that could make the folks leaving stick around the industry. But, if they've been successful and are mid career they may have priced themselves out of those opportunities.