The F1 press release is pretty transparent on that part:

"Over the course of this year, they have achieved operational milestones and made clear their commitment to brand the eleventh team GM/Cadillac, and that GM will enter as an engine supplier at a later time. Formula 1 is therefore pleased to move forward with this application process and will provide further updates in due course."

They are straight up saying that they approved the bid because of the team's branding being Cadillac and not Andretti. Which is a really weird statement IMO - do they actually have brand research numbers saying that Cadillac as a brand "brings more value"? Or are they really petty about not wanting the Andretti name in F1? Imo it's even possible that one of the Andrettis did something that isn't public and FOM is afraid that if it comes out it might taint the brand image of F1 if there is an Andretti team.