Maybe football will decline in the LT, but HS participation in football is still very strong. Here are the numbers of participants in 11-man HS football:
1969/1970: 853k
1983/1984: 923k
1996/1997: 957k
2003/2004: 1,033k
2009/2010: 1,109k
2010/2011: 1,110K
2014/2015: 1,085K
2017/2018: 1,070K
Yes, we keep hearing stories that football is in decline due to concussions and injuries, but people are still playing football and it is still the most popular sport. The sport has become safer at all levels today as practices are less intense and kids are taught the proper ways of tackling. If you live in the Northeast, your view of football is skewed as the school age population of most Northeast and Midwest states is declining which has resulted in football programs shuttering due to dwindling numbers.
I have a friend in Texas and when he moved to his town, they had 3 high schools, each with a football team. Today they have 7 high schools, each with a football team.