Why can't I use custom Teambuilder teams in Offline mode?

Something I've wanted to do for a while was play and develop my own league in franchise mode (Replacing all the teams and rosters of some of my own) and then just spectate games and simulate it all on it's own, solo. Yet, in Madden 26, it is impossible to use the custom teams I made and downloaded, in offline mode, only online mode. And even in online mode, I can't make multiple characters to swap between the teams. I have to retire a coach every week in order to watch and simulate CPU games.