As @Mavric said, Diaco coached the DL to push or squeeze the pocket, not to rush the QB. Playing your DBs so far off, and not requiring or wanting an effective pass rush, just from a schematic sense, is severely problematic.
Side Note: My goodness, in the last ~11 years we've had: Kevin Cosgrove, Mark Banker, and Bob Diaco as DCs. Three of the historically worst DCs of all time in the modern era have all been on Nebraska's coaching staff. It's sad enough to make you cry.
WRONG #fakenews
These guys sucked and we are glad that they will never be part of the NU staff again - however to say that they are three of the worst all time in college football is a bit much