"Liberty would not be 'denying their shareholders' anything! The absolute size of the pot is already fixed by the Concorde Agreement."
The Concorde Agreement limits the amount of revenue FOM can collect? I doubt that. I do imagine it dictates how the pot - whatever size it is - is distributed - and all evidence points to it being percentage based. No team boss ever complained bout team income being capped at a particular number. FOM is a public traded company so we can see it takes a little more than it gives all the teams. Whatever money Andretti's presence in F1 created for FOM a little more than half of that goes to Liberty's top line, and as you point out, adding Andretti wouldn't do bup-kiss to FOMs operating costs, so you could assume it really would go to their bottom line.
If FOM thought 'boy, having talked to corporate America, USGP, and ESPN having Andretti could boost our revenues 10%...' then they would tell the teams 'tough nuggets' and then turn to their shareholders and say "earnings per share +10%!! " Rather, I think FOM discovered the upside is far from being there and the reality is Andretti presents more financial risk to some team than brings benefits to the whole. And its not too hard to come to that conclusion.
I've been frank on this, I don't see Andretti as a qualified comer. I get the name is there, but the company as a racing team underperforms its size. How the f*** can't Colton Herta qualify for a super license? Honestly! It's hard to ignore McLaren came into their backyard and knocked them down a peg. I'm not sure how regular Indycar followers can say Andretti are in the same league as Penske, so if they aren't even at the pinnacle of Indycar why should they be at the pinnacle of circuit racing? And yes, that can go for other current F1 teams, but the times changed, Michael missed 2015.