because crew is a sizeable chunk of operating costs
but no where near as high as the insurance costs will become if the pilots are taken out of the aircraft and now add that to the cost of the ground controllers who will need the dual qualification of ATC and airline pilot to properly understand both aspects of a pilotless flight. The perceived financial gain simply isn't there. And I'll say it one more time, the security issues will prevent such flights unless all terrorist risk is removed.