Of the big 4 sports in the US/Canada the two oldest, baseball and hockey, developed pro leagues and farm leagues before they became big college sports and these have survived to this day, (minor league baseball and junior hockey).
The other 2 sports, football and basketball, were big college sports before they became big pro sports and hence a suitable farm league system never developed. Both sports are mostly happy to see the existing system continue as it would be difficult to build equivalent minor leagues from scratch.
Logistics in football don’t led itself to a farm league.(See all failed alternative leagues tried) Cost is the #1 prohibitive factor, you have 50+ man rosters, Baseball and Hockey have 1/2 of that and you have more trainers, equipment costs, medical staff, etc in football than both those sports. Plus to sound all patrician about football. People just won’t go to see farm league talent in football for the game’s sake(See basketball also). Farm league baseball and hockey are light years behind NHL and MLB talent. What .75% of MLB farm guys ever make it to the Show. People on a hot Summer afternoon will pay $15 and $4 for a hotdog to watch baseball, even if it’s played sloppily. Same goes for hockey. Football, no way. College football is a different animal, it has cultural roots in America and a regional pride by it’s fan bases. College hockey and baseball are sports between football and basketball season.
Football is very costly, basketball relatively cheap. There used to be semi-pro teams representing towns or companies in our area. I remember a game in 1960 between the Jersey Sharks and the Franklin Miners (Franklin, NJ or PA, not clear which) played on the infield of our local stock car track. Attendance was sparse, it started raining, and defense ruled in a 6-0 slugfest.
To try to confirm my memories I searched for the game in the 'net archives, and surprise! The Sharks were revived in 2017. This the mission statement from their website:
The JERSEY SHARKS football nonprofit organization was established in 2017. Our program has built and sustained adult amateur football within a safe and competitive environment for young adults who wish to continue their football careers and who are willing to contribute to the community.