GT, FORZA, MK are the flagship race games for each console.

But there are tons of racing games out there that are just as awesome!

For the car maniacs there are also WRC, NfS, F1 and Nascar For consoles or pc and Colin McRae Rally for iOS, sports care challenge for iOS and android!

Classics like Carmageddon and burnout which give you nice rewards for crashing or killing pedestrians

For those that wanna race with something else then cars there are MotoGP, Wave Race, Hydro Thunder.

But mainly we have cars, which is great but why can't we have more diversity?

Or am i totally missing some awesome racers that i should be playing right now?

I think theres more than enough diversity in the racing genre.
Dont forget wipeout

Sonic & All-Stars Racing Transformed -> Best kart game right now
The Dirt series
The Motorstorm series (especially Apocalypse, which is unique)
Blur aka Mario Kart with real cars and "realistic" physics.
Split Second
Shift series
Grid series
Driveclub

That's all I can think right now, but there is enough diversity!

I hope Motorstorm comes back, I was just playing the first one again.

Also a proper rally game, not that Dirt abomination.
I enjoyed WRC 3, but it left me wanting more. Colin McRay used to be the one to get.

Midnight club LA was awesome too, that series has also gone quiet :/

Wipeout needs to come back, re-open studio Liverpool please.

Driver SF turned out to be very enjoyable after all the backlash.

SSX, the last one wasn't as good as SSX 3, but there is still room for a snow board racer.

What happened to the downhill BMX games, they didn't make an appearance last gen.

Futuristic (high speed and usually "magnetic" track based: Extreme G, F-Zero, WipEout, Star Wars Ep1 Racer, FAST.

Snowboarding games often have a racing focus (could be put into sports category along with Wave Race as a genre but the game mechanics are very different)

You didn't mention many other kart racers (Crash, DKR, LBP, ModNation)

There are top down racers like Micro Machines, not sure what sub-category they might fit into other than their own.

And an unusual one could be Light Trax (WiiWare), in which you race beams of light.

!!SSX, last one hasn't been to long ago has it? I still remember SSX Tricky quite well

Mario Kart is my fav, along with Need for Speed for an arcadey semi-realistic racer (mainly Hot Pursuit types).

I also really liked Excite Truck, Excitebots, and MotorStorm.

I was never a fan of overly realistic ones like GT and Forza. I tried Blur once. It was nice. I always meant to try Wipeout, but never did :(

Everyone is forgetting the best racing game of all times.

SARPBC

The fact that you have to look up this abbreviation proves its unpopularity :(

Sonic all Stars and Need for Speed Rivals are both excellent games.

Motosports games are one of my favorite, there is plenty of diversity GT, MX vs ATV, Dirt, F1, and Moto GP just a few all are great. There are good games from pretty much every racing venue.