It's much harder to find a good Linux admin than a good Windows admin. A good Linux admin also costs more than a good Windows admin. A good Linux admin is not nearly as uniform in how they implement their environments than a good Windows admin. Basically, Windows admins are cheaper, easier to replace without a complete reevaluation of the existing implementation, and Windows has better enterprise support to boot.
As someone who works in the public sector, I can tell you that the pay of the public sector does not attract good Linux admins. They'd rather go work for companies that will pay more handsomely for their services, like financial companies, biotechs, etc(where I live, at least).