re: How did Nebraska used to be a dominant football program?

It was a lot less competitive back then. The Florida schools were just become relevant when Nebraska was already in rhythm and recruiting there. Penn State and Pitt were the only viable local options for East Coast recruits in the 70s. And UCLA, USC and Washington were largely the most competitive West Coast teams.

So it was easier for a team like Nebraska to go all-in in those recruiting hotbeds. Now they're just another team.