By limiting the number of players available on game day, the league prevents wealthier teams from "stockpiling" excessive talent, which could create an unfair advantage over teams with smaller budgets.
The collective bargaining agreement (CBA) between the NFL and the Players Association (NFLPA) structures contracts with various bonuses, including "active roster bonuses" for players who are dressed for a game. Limiting the game-day roster helps manage salary cap implications and associated bonus payments.