sicilian scheveningen

i like move move 12.Rad1 in this position.

can someone  explain reason behind why 12.Rae1 is popular move?

thanks, that might be the case.

and yes note myself: I sholud focus more on opponents counterplay.

The rook is more valuable on e1 rather than d1. If the e pawn or f pawn advances the files may open so the rooks are better there, there is no point in this position to attack d6. Plus you have 2 minor pieces in the way on the d file that aren't going to move anywhere. The knight is strong and bishop to e2 is a waste of a tempo. It also makes it harder for black to break in the center with d5 (since the file opens). Where the rooks go is pretty important, as if you put them on the wrong squares they become useless (or not as effective).

the rook aids white's kingside attack better on e1

I think you have something wrong. It should say 6.g4!! and not 6.f4??

why is it so?

6. f4 is normal

Im not an authority on the Scheveningen but I think either the Keres Attack or the English give you better chances. 

But to be honest, I was just joking around, play whichever move you like, as long as you are comfortable with it.