IMO you're right in some situations about the player either being a) poorly evaluated and/or b) under developed, but another big problem is just talent retention. Another phrase I like to use is the "roster boss." It's not a problem specific to Nebraska, either. It's pretty much a universal issue that's been happening for awhile but got worse once the transfer portal became a thing.I don't follow recruiting that closely, but based on final rankings, NU has had to have plenty of 4-star recruits and a few 5-stars. The problem is they have either been overrated out of HS, or haven't been developed by previous staffs.
Basically, if we go back and look at some of Nebraska's recruiting classes from the last 5-10 years, it's eye-opening just how many players either didn't make a significant impact and/or transferred out of the program. Obviously attrition is going to happen but they just seem to have way more misses than hits.