In a word: Licensing .
In a few words:
Complicating matters further, in most cases, developers are actually paying auto manufactures to include their cars in games. Ford confirmed game licensing actually generated revenue for the company. But if Ford really wanted a car in a game that wasn’t going to make the cut—Mustangs are no doubt a sexier sell than a Ford ST—the roles would reverse, and Ford would pay the developer to “subsidize” that placement.
Ford reports these in-game advertisements are extremely worthwhile to their brand. In research conducted by Interpret, they discovered that participants of an in-game Ford ad exposure saw:
In summary: Car manufacturer tells Turn 10 “we will let you have [desirable car] if you also include [less desirable car] and [alternate version of car] as well.”