Having been a full-time DBA for many years, and having worked myself out of more than one job, I'm going to suggest that many companies do not want to hire a full-time DBA. They really want to hire an expert part-time DBA, someone who can solve their immediate problems, then bring their servers to the status of maintenance mode, where everything is working like a finely tuned machine. That same DBA can make himself/herself available for emergencies and catastrophic failures on an as-needed basis, and an occasional server tune-up. He/she can perform some regular monitoring of database server metrics to intercept as-yet-undetectable problems before they become actual problems. Many budding problems give early warning signals if you know what to look for.