"Because it's always been done that way, and that's what the regulations say," will not be accepted, at least not by me.
(Really, my question is more like why humans will still be needed in the loop in 2036. If we started automating ATC today, that's probably how long it would take to cut over to the new system.)
If these are just "excuses" and not "reasons," then explain how you have determined them as such.