Dominik D
Regular
They may not want to deal with logistics involved (they have facilities in UK and US and Ferrari is based in Maranello). It may not be very profitable unless Cadillac decides to buy more parts from them. Or, conversely, they may not want to sell anything beyond engine and Cadillac may be shopping for more than just PU. There's always a risk of another team being able to poach talent easier by having direct relationship with you team. And so on.Why wouldn't Ferrari provide for another team? Are they afraid a new team would beat them? It's not going to hurt Ferrari, just give them more money. Andretti has a 5 decades long relationship with Ferrari, I don't see them saying no. Andretti has said they aren't even talking to other potential providers.
What I'm trying to say is that it's not like gaining customer for your engine is a full on positive (or even neutral) event. There are costs and risks involved, even if the customer brings you some cash (which Ferrari doesn't really need). Worth noting that UK facilities Andretti operates are across the street from Aston so it may be easier to find talent familiar with Mercedes engines (but it's unlikely Merc would provide given how many customers they already have).