I think the simple answer is supply and demand. It is easy enough to get someone who can click around in the tools and get stuff done without doing too much damage. It’s not so easy to find someone who can make sure that you can depend of having your servers up, secure, optimized, backed up, and ready to recover from a disaster. Throw in the ability to work with developers to show them how to optimize queries and design a database, and you have someone with real value. In my experience, full capability database administrators are in far shorter supply than developers with some admin experience. As with anything else, short supply and high demand drive the price up.