The question is quite simple : Why everyone in the video game's industry is so secret ? 

- Dev almost never speak out the budget of the devlopment. Even indies one barely speak about it. As far as I remember only dustforce's one and Phil Fish has openly speak about it while being the most precise they could.
- Editors never speak about how much they grossed on a specific game. They'll always speak about general grossing, or you can find it by yourself, but you'll never find any information about specific game gross.
- Heck, they barely told us the difference between "sold" and "shipped".
- Sony tell us 4.2 m of PS4, but they refuse to give any numbers per contry or side of the world. Same goes for Microsoft. 

And we can go this way long enough.

We're on Vgchartz and we all know how hard it is to precisely know how many copies each game sold. 

So, does anybody know the reason behing the need of this level of "secret" ?

Secrecy gives an advantage. You can fudge numbers, create better outlooks for your fans, impress potential investors, change your image to closer fit what you want it to be. Give up all your information and you're naked.

They don't have anyone to answer too, because gaming media is so weak and easily swayed.

Because third parties are plotting to destroy you know who and you don't go in the open when you are plotting

because EA might see you doing well?

a) Why do you think you have a right to know?
b) Why does your spelling and grammar suck so much?

Because the industry is not as healthy as advertised outside of the top few franchises.

If they refuse to breakdown game grosses, it's because most of them didn't profit
If Sony refuses a country breakdown, it's because it would show weaknesses

why you seriously fussed about b?

Because no one cares about video games. 

Yea... except those millions upon millions of fans who do but fuck them right? -.-