Maybe he thinks bishops are worth more than rooks. 
Why do beginers play this?
I know they know that, and they still play it, even after 1000 times I captured their rooks like that.
Many beginners bring their Rooks out like that, they think that's how it's done, and they really don't know that a Rook is worth more than a Bishop.
Bishops r 3 and rooks r 5. Plus u cant checkmate with a king
and bishop but u could with a king and rook
Beginners, real beginners, don't even know how to checkmate with e.g. K+Q vs K. So the relative values represent a sort of theoretical or symbolic... or in any case impractical system. After all you can't lose a whole game just because you lose a few pieces right?
So they start the game with the pieces that have the simplest move set and are highly mobile: the rooks. Some start with the queen, but even people who can't spell chess know that the queen is valuable and you dont want to lose her.
Anyway, in fact moving the rooks outside the pawns on the 3rd rank, where they can immediately attack anywhere, is very reasonable and logical if you don't know anything about the game. They instinctively increase mobility and flexibility of attack. Not bad.
(Then they continue to do it out of habit, and it might work on 80% of their opponents. It doesn't work on you, but they don't know any other opening. This sort of behavior is perhaps not a bad description of most amateur players lol)
It's definitely common. 2 reasons I can think of...
1. The rook's movement is the easiest to understand.
2. They are unaware of the value of the pieces.
This is something I draw attention to actually in my "Beginner to Chess Master" series.
Video #2 to be exact:
Is it really that common? I didn't make moves that bad even when I was 6 years old. No joke.
ChessNetwork wrote:
It's definitely common. 2 reasons I can think of...
1. The rook's movement is the easiest to understand.
2. They are unaware of the value of the pieces.
This is something I draw attention to actually in my "Beginner to Chess Master" series.
Video #2 to be exact:
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I know that they think they should get their rooks out, but even after one rook was easily taken, THEY STILL DO THE SAME THING!!!!!! Learning from your mistakes and not doing them mutiple times doesn't just apply to chess, it also applies to a lot of other things, and the next game, they do the same thing over and over again.