It isn't just the "no", it's the fact Andretti has jumped through every single hoop. They have racing heritage, a reputation they want to keep and even went to lengths to bring new partners to the sport and some enthusiasm. FOM set a ridiculous "anti dilution" fee expecting no one to want to enter and Andretti called their bluff. When you have billionaires willing to paint back marker teams in the colours of a nation or own whole teams to keep their kids happy, the amount of "investment firms" who have dabbled and lost, it makes a change where someone wants to go racing because it's racing. This is probably why FOM rejected them because they were in for the sport and not the spectacle.
The driver market is crying out for 12+ teams, let Andretti in and another owned by a crazy billionaire and compare how competitive both would be. In all competition there's always a winner and there has to be someone last.