Caleb Williams spent his Saturday running through 60-plus plays in a private morning workout at Soldier Field last weekend. A few hours later, paying customers watched his backups on the Chicago Bears play the Cleveland Browns.If there is a clear explanation of what preseason football has become, this is it. The work that the Bears considered to be most valuable was closed to the public. The product it sold was the audition.Preseason football has developed into a class system. Established stars increasingly receive their most valuable work in private, controlled environments. Secure starters play sparingly, if at all. Players with the smallest contracts and the least job security supply most of the snaps, contact and physical risk in games from which the league continues to profit.To fans all across the country, preseason is packaged and sold as NFL games. For the majority of those participating, it is a job interview with tackling.That the Bears essentially chose a private practice over that afternoon’s game as the best preparation for their franchise quarterback isn’t surprising. Teams across the league are making those same decisions all this month.As the Browns and Buffalo Bills prepared to meet Saturday, both head coaches agreed the starters wouldn’t play much, if at all, in the game because of the work they got in during Thursday’s joint practice. This comes after Josh Allen played only 15 snaps in the Bills’ preseason opener — which is 15 more than he took in last year’s entire preseason.We’ve come a long way from the NFL’s barnstorming tours of 50 years ago, when teams would play six preseason games at various stops across the country, including some neutral fields.The value has migrated. The games are becoming less useful to the players who fans want to watch and more important to the ones most fans don’t know.For players fighting for jobs, it creates a cruel conundrum: The same game that can launch a career can also end one.Houston quarterback Graham Mertz tore his ACL in the Texans’ opener and is out for the season. He has never appeared in a regular-season game and was competing for a backup job.