If I recall, back when Trev Alberts was part of the show, they really, really didn't like each other and the vitriol has remained even years after Trev moved on.
It's this. Alberts was a blatant homer when they worked together and it was apparent that the two didn't like each other. May took every opportunity to rankle Alberts over Nebraska's decline. I don't generally buy into persecution theories, but May just doesn't like Nebraska. Aside from this, I pay little attention to May as he just isn't very insightful about college football in general.