
As with every Forza game Turn 10’s sim racer, released in 2015, Forza Motorsport 6 will be delisted on September 15th. Racing games are filled with all kinds of licensing. There is a bunch of licensed cars and music in both the Motorsport and the Horizon titles. After, it seems, 4 years the licensing deals for these games expire.
Because of the expired licensing, Microsoft has already put Forza Motorsport 6 on this months Games with Gold. In addition to this Microsoft has now put a discount on the DLC.

Microsoft is now offering the Forza Motorsport 6 Complete Add-on Collection for $4,99, which means the DLC bundle is 95% off. Included in this bundle are the NASCAR expansion, the Mobil1 Car Pack, the Hot Wheels Car Pack and a lot more.
If Forza Horizon 3 has the same licensing deal, we can expect that game to be delisted by September 2020. You are still able to play, and download, the game after the game gets delisted from the Microsoft Store.