I agree, Hoiberg has done a shitty job outside of last year, but I think you are oversimplifying the idea that "it really isn't that hard for a power conference team to make the NCAA tournament." There are only 37 spots available for at-large teams once all the conference tournament champions are in. The P5 will generally get the most bids and send the most teams, but that still requires to finish generally in the upper half of your conference, but that doesn't guarantee a spot.
Below are the 37 projected at-large bids for this year, leaving only 34 P5 at-large spots available—making the path to the NCAA Tournament pretty tough, even for P5 programs. If it were truly "easy," teams with richer basketball histories than NU like Louisville (last appearance: 2019), Utah (2016), Wake Forest (2017), Butler (2018), Cincinnati (2019), and St. John’s (2019) would be making the tournament consistently.
The only P5 schools with fewer all-time bids than Nebraska (8) are Northwestern (3) and UCF (5). UCF wasn't D1 until 1985.
Projected
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Now if you were to say that making your conference tournament should be easy, which Nebraska failed to do, I would totally agree with you.