To get the ball rolling, Andretti had already signed a preliminary contract with Renault years ago. But that expired in March 2023. And at the moment, the French are showing no great desire to resume negotiations on a continuation. Renault, alias Alpine, does not want to get caught in the crossfire of a power struggle between the FIA and FOM.
It could be that they know they will be required to anyway, so no point sticking their head above the parapet by making a new deal before they have to.
The requirement will only be there for 2025. For 2026 there will be three engine suppliers with only one team, Alpine/Renault, Audi, and Honda but Honda is GM’s IndyCar competitor, so that one is ruled out.