Is something wrong with it coming out every two years? 

Franchise fatigue. It hits the best of them. Just look at the reasons why MLB The Show is getting 70's and 80's, even though it is being called a very good game.

"Failure to innovate".

Not every franchise can add weather and have everyone be like "OMG, innovation in the series", even though it is only because they are basically the last to do so.

You kind of answered the question yourself. If recognized brands like Fifa and COD could make good numbers, why would suddenly one of the biggest brands ever (GT6) fall short? What, did all racing fans all of a sudden become so blinded by the PS4 that they forgot GT6, or could it be that Sony simply did not marklet it? If GT is dependent on hardware release to sell good, it is in deep trouble. Luckily, GT5 showed that when Sony tries, those games will sell good and have long legs.

As Sony and Nintendo have proven, the best racers take time to develop. They will have you covered for quite a while if you're patient. What Microsoft is doing with Forza ensures lower sales than what Sony or Nintendo are used to in racers.Microsoft has Forza on a two year cycle.

Forza sim is on a 2 year cycle, but the franchise itself "Forza" is yearly.

Gran Turismo as a launch title would have been huge! Oh well now they can focus on improving their car models/engine sounds etc so they aren't re-skins of PS2 versions. That's my biggest gripe

Hmm fair enough, I imagine series fatigue will eventually hit Forza. Hopefully soon so it forces MS to let Turn 10 do something else. (would still be a racing game most likely since that's all they know.

Which is why I like when companies do not do annual releases.

Would be nice to see what else Turn 10 can do.

Even worse. If Sony announced GT7 for 2017 with a prologue people would be chomping at the bit (since they would have to wait two more years). They can also use the feedback to tweak the game into the dream Forza since the gaming world has become a little more transparent after GT5. Microsoft has the same issue as Activision with the western business model of releasing games yearly or twice a year. I am thankful that Sony is stepping back from that old mentality because Yoshida hates annual games.

it really was, putting so close to the PS4 launch really eclipsed that sales, even a cross-gen release would've been more beneficial