The population in and around Omaha and Lincoln, where Democrats are making big gains, is exploding out of control while it's decreasing if not completely collapsing almost everywhere else, where Republicans have little room to improve anyway since they already dominate the rest of the state. Look at this map of population growth since the last census:
Nebraska will continue to trend leftward, but don't expect Democrats to win anytime soon unless the party figures out how to appeal to rural America.
While the metro areas in the eastern portion of the state are obviously growing faster than the state average, those county results actually appear pretty random...