They are? Or the other teams are? Another team on the grid means everyone else takes a cut in $$$
Part of Andretti's buy-in is $200 million compensation to be split among the other teams.
From an AP article:
Liberty Media holds the F1 commercial rights and it is to the corporate giant that Andretti Global and partner Cadillac must next prove their commercial value. Liberty Media and F1 President Stefano Domenicali have mostly sided with the existing 10 teams, which vehemently oppose expanding the 20-car grid. The teams, however, have no vote on expansion.
Snip...
Current F1 teams — namely top players Red Bull and Mercedes — argue they have invested too much into F1 for someone to buy their way into the series. There is a $200 million anti-dilution fee for any new entrant, but the teams have argued expansion takes away from their financial cut.