Why USA series and movies shows fake operating systems and software interfaces?

Patents my friend patents! And also ads for any product aren't free! Companies have to pay advertising fees for their products to show up in movies, tv shows!

Because they can show those things without spending the money on that kind of thing, so they show.  

For earning money

It's a combination of having something that looks clean\sharp on camera and not wanting to give free endorsements to Microsoft or Apple.    Your typical computer will have a lot of detail and graphics on screen that will look far too busy on a camera shot.  

Sometimes it's because they are worried about trademarks and intellectual property. By avoiding anything recognizable they are less likely to be sued for violating a copyright or associating a product with evil.

the whole idea is making money fast so they fake anything to get cash 

Here in the Netherlands most series use real operating systems.

They may be fake but the interfaces usually like cool and easy to understand. Its all for us, the audience. 

Most of them are concepts that may actually happen in the future

That's because what they're trying to show doesn't happen in real life. Best example? When they zoom in a frozen frame from a CCTV camera, the image magically becomes clearer and sharper. In reality, it's the opposite.

It has to do with "product placement"! Some times we get a good clue, I think in War Games it shows an apple computer. I don't know how much it cost Apple to get that moment on screen or if it did. It is my guess it did. I suggest this because Reece's paid to have their candy used in ET.

If a company is approached about paying for placement and they decline, the movie producer has little choice but to make up a generic or totally unauthentic representation.