Here is a graph showing how well or bad is performing each of the major racing franchise in retail lately. This comparison is for racing genre at large so needless to point out the difference between racing simulator and arcade racing. This graph is only to see the trend in the major racing franchises of the Big 3.

A few comment on this:

- After the huge drop between MK7 and MK8, due mostly to the low userbase the Wii U had, Mario Kart franchise seems to be on the right track to reach once again 15M+ numbers, quite a feat considering MK8D is an enhanced port. This latest entry in the franchise will continue charting in the top 10 for a long time again given there is no indication a MK9 will be released anytime soon. I won't be surprised to see it reached 20M at some point.

- For the past 10 years or so, GT franchise is on a downhill saleswise. GTS, the latest entry, barely managed so far to sell as much as GT6 did, which was released at the end of PS3 lifecycle when all eyes were on the PS4. 29 weeks after its release, GTS is not charting well either, being currently at no. 61 in the global weekly chart. The only possible way of reversing this trend would be to release GT7 on PS5 since a late release in PS4's lifecycle would imply low numbers as well.

- Releasing a new Forza every year is not helping the franchise doing great numbers. When Forza titles were released every two years, sales were averaging 5M while now sales of each title are averaging 2M. Sure the userbase of the X1 is not helping either.

MK8 Deluxe os definitely reaching 20m+. It just keeps selling. I mean, it’s probably around 3m this year alone, and there’s a full semester still to go, not to mention the holidays.

Forza is also on PC btw.

Horizon 3 was a sales success, looks like.
https://www.windowscentral.com/forza-horizon-3-crosses-9-million-players-xbox-one-and-pc

The sales of Mario Kart Wii and DS... just wow. I wonder if MK8Deluxe can beat DS sales.

GT's decline is sad sight to see, namely how awesome the franchise was long time ago. Also wondering if MK8 should be combined with MK8D, since most treat it like a port on this site.

Pretty clear that the racing genre is one of the genres to lose the most marketshare as each year goes by. RTS too, but that genre was never too big.

I wonder if since MK8D is selling so well, that Nintendo holds off on 9 until their next hardware system. Seriously, it's gonna hit 14+M if it keeps going like this.

Nintendo is playing things smart by only releasing one Mario Kart on each of their consoles, although it'll be interesting to see if Switch is going to change things since the one it has is essentially just an update port.

Gran Turismo on the other hand is a prime example of a mishandled property, which is actually quite unusual for Sony. The series seemed to have lost a lot of steam when GT5 took such a long time to come out, and then the following releases have never really gotten the spotlight put on them like the earlier games did.

Forza needs to pace out their releases better. Releasing new game every single year seems to be causing a lot of fatigue and lack of excitement in fans.

I was hesitating to combine their sales but since it is on a new system and it has been released 3 years after, I decided to consider it as a disctinct entry.

GTS is in a weird position. They banked heavily on the online component, which is great btw. Yet the online user base is only a very small percentage of its sales.

Sport Races finished % of Players Players Count
A. 0 Races 75% 3,389,000
B. 1-10 Races 16% 723,800
C. 11-20 Races 3% 116,500
D. More than 20 Races 6% 276,700

PD hastily added more single player content (and is still adding) yet the perception of it being an online title (not helped by having to be online to save progress) has already been cemented.

There's about 30 to 40 thousand active online players currently, so still healthy and seems to be stabilizing. It's not growing though.
http://www.kudosprime.com/gts/stats.php?stat_preset=daily_sport_activity