Not all of them. Some become ambassadors by working up from the ranks. Yes, they are still appointed, but these are appointed by merit. I have known Management Officers that have worked their way up to Ambassador in several instances. But, the point is that those two, Romney and Petraeus are not good choices. There are career State Dept employees that have experience and ability to perform a great job in that position as SecState.

Petraeus is hardly better than Hillary, a criminal
Romney is a petulant loser with no loyalty.