Many of these athletes are going to camps. The biggest issue with Nebraska high school sports, and those from other less populated states is coaching and player development.
Don't get me wrong, there are some good coaches out there, but some of the best coaches leave the state or do something else because Nebraska high school coaches don't get paid well.
Andrew Shanle is coaching down here in Houston area, I would bet he is making 80 to 100k to only coach football and not teach a single subject. Plus he has a football period for varsity and another for sub varsity players. I know my high school coach was teaching 6 periods of English, had a single conference period, and we were limited to 2 hours after school, and could only practice during season.
So the draw to go somewhere else is huge. So what happens is states that pay more, get better coaches, The other thing is player development. Many of those camps used to just gauge athleticism. 40 times, cone drills, etc.. now they have linemen challenges and 1 on 1 drills where kids from other states, with excellent coaching, have been taught the finer points of blocking or pass rushing technique and don't just rely on their God given abilities. Then population factors in, I know I have written this before but some of the high schools in Houston or Dallas will put out more P5 players in a season than the entire state of Nebraska does. So each day those kids are going against other P5 players in practice. So when they do go to camps, they just look better than other kids do.
The down side to that, from a recruiting standpoint, is that sometimes, those players from California, Texas, Florida or other recruiting hotbeds have reached their peak or are very close to their ceiling when they get to college. So they are better ready to play immediately but since they are near their peak, you don't see the amount of improvement that you see from a more raw player.