I believe there are several factors playing into this, some you mentioned.
Club Sports are a part of the problem. If a family is not able to or doesn't want to get their kids involved in Club Sports at a young age, they fall so far behind that they can't catch up. I know, people are going to start giving examples of guys that played 1 year of HS Football and went on to the NFL. Those are outliers, and clearly not the normal. This goes for Pee Wee football, Youth Wrestling, etc, not just "Elite Club Sports".
Youth Coaches are another part of the problem. A youth football coach can wreck an undersized and timid 5th grade boy in a hurry. They demoralize these youngsters, they typically fall into a favoritism pattern centered around their own personal friends, and place far too much emphasis on winning rather than development. Development is a very misunderstood term right now because of our Husker Football situation. Player development at the youth level is not just physical skill building. Not nearly enough time is spent on philosophy and strategy. It is important that kids understand the big picture. Simply put, too many youth coaches are focused on winning when their PRIMARY GOAL needs to be to keep every one of those kids coming back every single year. They come back because the understand the sport which helps them fall in love.
Time demands cause a great deal of challenge as well. Summer activities such as Baseball, Softball, 4-H, and scouts will typically get run over by School sports. Weight Lifting, Team Camp, Individual Workouts, 7 on 7, and Y-League Basketball are some examples. Many times the parents are the ones that finally say no more. The parents want to camp and vacation. It amazes me the number of families that take vacation in late July and early August because that is the first time that they had a chance to even think about it.
Household Demographics is another big part of the problem. We are seeing more migrant families moving into our communities. Many of our sports programs are not familiar to them. It is challenging to create a welcoming culture that invites these families into a sport that they are not familiar with while also navigating the language barrier.
Single parent homes fall into this as well. It is a natural assumption that single parents don't have enough money to involve their kids in extracurricular activities. Money isn't the biggest factor here, it is time. The parent that is raising these kids is working full time, trying to cover homework, household duties, and also have a life. It is very challenging to find the time to support even more.
Football related, but Nebraska kids don't grow up caring about Nebraska football anymore. Nebraska football has become nothing more than a pissing post for our fan base's loudest voice. It is mostly negativity and that doesn't equate to kids growing up wanting to play football. It is quite the opposite.
Diminishing numbers are creating a spiral effect in the smaller communities. Because there are only 16 kids out for football, the Freshmen have no choice but to play. There is no JV Football, so all of the 7th and 8th grade boys get to watch their Freshmen buddies get hurt on Friday night. They show up Monday in walking boots, dislocated shoulders, concussion protocol, broken arms, and the rare treat of getting to watch them get hauled off in an Ambulance on Friday night. No, these youngsters are not interested in being thrown to the wolves.
This list could go on and on. It is complicated. I believe the biggest contributor is Youth Coaches.