I posted my dumb theory elsewhere and it's just a guess, but I see two possible factors that could be biasing Shanle whether he realizes it or not.
Shanle played his pro career primarily in New Orleans, and ended there. Judging by his social media, he seemed to have adopted LA as a second home, and IIRC has tweeted a lot about LSU. So first, not only is Mickey a former Husker, but a NOLA native and LSU assistant coach, obviously.
Second, Rhule coached for his NFC South rival Carolina. Would Shanle be as concerned if he coached at Cleveland and failed? Maybe, maybe not, just a rhetorical question.
If Mickey had been named head coach, I would have been able to rationalize it to myself and be on board. But if an available guy has D1 and power 5 head coaching experience with some good seasons in there, you have to try that before handing it to a guy with two seasons as head coach at an NAIA team with not good results and then a 3-6 interim stint. There isn't much logical reason to support hiring Mickey but not willing to give Rhule a fair chance.