If you look in the fine print, the warranties are often third party insurance companies. And the financing bank is often the OEM! And the dealer also has its inventory on credit, and the creditor is also often the OEM. Yes, there's a web of entities and transactions going on, but at some level that's accounting. You pay a monthly fee in exchange for use of the car. Making this deal with a whole ecosystem may or may not be better than making it directly with the OEM.