The problem with the "It's Nebraska" handwaving is that he's not doing poorly relative to college basketball or power conference teams. If this is his last year, the Hoiberg era will be the worst at least going back to WWII in the history of Nebraska. So he's horrible relative to Nebrasketball history.
As for the "can't get players" argument, if you dropped McGowen and Breidenbach (who just went down for the year the past game) into ISU, they would be the #1 and #11 all-time highest ranked players at ISU as far back as 247 tracks that, which looks like nearly 20 years. In fact, 8 of the top 20 recruits on 247 have occurred since Fred arrived. A couple have transferred out, and clearly some/most haven't panned out. But he's actually recruited to Nebraska well relative to its history.
It's clearly a hard job with no history, and there isn't a ton of talent there. But there's a lot more wrong than just "you can't win at Nebraska in hoops." No doubt it's difficult, but he's managing to fail at a rate no one else at Nebraska has for at least 80 years. That's something.