It's easy to think of the Forza Motorsport series as an afterthought or an "oh yeah," type of game, since it doesn't fit in with our modern conception of a AAA game. That being said, they're apparently incredibly profitable.
Turn 10 Studios, primary developer of most games in the franchise, announced today that the Forza series as a whole has passed $1 billion (with a b) in worldwide sales. This was aided in no small part by last fall's Forza Horizon 3, which has sold more than $2.5 million units (and counting).
'We'd like to thank our amazing fans and partners for their continued support and we can't wait for you to see what 2017 will bring," Turn 10 Studios said in their announcement.
Of course, this announcement comes shortly after Playground Games (the primary developer of Forza Horizon 3) was revealed to be working on a much different non-racing game. So, it's possible that Turn 10 Studios will be taking full control of the series' next installment.
In the mean time, though, a billion is a lot of money.