The reason the titan still sells for 1K is because it has something like 24x compute performance than the 780 ti, although it's far inferior in typical gaming workloads. It's now in the vein of workstation graphics cards. I should mention though, nvidia chose to limit the 780 ti's compute performance purposefully, so they could continue to sell the titan, similarly to how intel arbitrarily locks some of their processor models for no reason except because they can and it will make them more money