An artifact of the Cold War when we needed Turkey for (1) bases and listening posts geographically close to the USSR and (2) Turkey had one of the largest standing armies in the world, in case things ever got hot with the USSR. Now, we still want Incirlik. Otherwise, I don't know.
“An artifact of the Cold War when.....”
It goes back much further than that. The western European countries kept the Ottomans in place to keep the Russians out of the Mediterranean.