If you have a copy of Madden 25, customize the rosters before launching into CFM and release a few high profile players into the FA pool. Once you've done that, start a new CFM and try signing those players (with Salary Cap disabled). I guarantee that you will be able to sign them, regardless of signing bonus (even if it places your funds in the negative). Now try the same process in Madden 15; it won't work.
Sure, signing bonuses being deducted from your overall revenue is "realistic", but disabling the salary cap
isn't realistic, so why is this rule still imposed on those who disable the salary cap? The whole premise of disabling the salary cap is having unlimited funds. There is no possibility of doing a fantasy draft or rebuilding a franchise that desperately needs a new stadium without having to watch your starters leave in mass exodus at the start of the second season, in Madden 15. This is a game-breaking flaw. EA has never really managed to get the salary cap feature tuned correctly, mostly because contracts aren't as one-dimensional as an overall value and a signing bonus. There are incentives, clauses, etc that help protect teams from reaching beyond their cap. They removed the option for back-ended contracts in Madden 25 and that was really the final nail in the coffin for a salary cap enabled CFM.