Andretti is an established racing team that has already proven ambitious and successful in other disciplines, and has demonstrated a clear and strong interest in F1 specifically. Gene Haas essentially got talked into starting his team, is by all accounts not that invested and mostly cares about the free advertising for his CNC machines. I'm sure Americans would prefer a team prepared to invest money into the sport instead of one struggling to even approach the budget cap and resorting to cut the pitwall to three people to save resources.

Who on the grid does? Ferrari, Alpine, Honda, and Mercedes build engines, outside of that the rest of the teams are building tightly regulated cars. Andretti is one of the biggest names in American motorsport, they're attempting to bring in a new engine supplier and one of the biggest car companies in the world, and they have the money to do it. What more can be reasonably asked of them?