How come they changed Ventus from left handed to right handed. In the secret ending of Kingdom Hearts 2 Ventus is definitely left handed but when the game got released he was right handed just like the rest. This would have been a good start to also have some left handed keyblade warriors in the franchise but why did they change him.

That FMV was made by a completely different team.

because left handed dies fast nah JK idk why either

The same reason of making the keyblade's teeth inward? 

I think that Nomura once said that most KH characters are ambidextrous but just prefer to use their right hand. Meaning that, theoretically, they are able to fight just as well with their other hand, we just don't see them do it.

Clearly the team didn't bother with the source material.  A lot more fans tend to care about handedness than developers.