Ruy Exchange--Why not 4...bxc6?

The Ruy Lopez Exchanges goes like this: e4 e5 Nf3 Nc6 Bb5 a6 Bxc6. After this black's most common response is 4...dxc6, but that takes away from the center! What is the reason few people play 4...bxc6, taking toward the center?

i think its because black then will have 3 pawn islands, the a pawn will become weak and the bishops will have less mobility

dxc6 means that both bishops have open lines, as does the queen. It also allows ...Qd4 if Nxe5, whereas bxc6 forces ...Qe7 where the pawn can just about be protected with f4?!

It doesn't really take away from the center, the pawn on c6 still controls the d5 square.  It also solidifies the queenside position for black and allows for 0-0-0.  I've never understood why anyone would ever play the Ruy Exchange, throwing away the precious light-squared bishop for basically nothing.  

After 5. Nxe5, what is Black's response?

5. ...Qe7?

5...Qd4.  

according to the video i watched its because white wants to win with the kingside majority because it can build a passer while black queens majority can´t.

Anyway for the other who might be reading this, but that still doesnt make Fischer and endgame player

Don't get me wrong, I don't consider Bxc6 a blunder, I just don't think it plays to white's advantage as much as Ba4.  Black's job is to just play aggressively if white plays the exchange variation and refuse other piece exchanges.  

You might be overestimating white's light squared bishop. Giving it away for a better pawn structure is a totally reasonable choice: with a passed pawn you can win the game.

And to answer the previous question, after Nxe5 black would play Qg5.

The queens don't always come off in the Ruy exchange.

However most games go like this.

It is well known that the more pieces that come off in this line, the better for white. This is why in must win situations where my opponent is very happy with a draw, I play the exchange as white. The point is that since black shouldn't trade pieces, more will remain on and I will be able to make the game a complicated fight! (Clever, huh? :-) However, that is the only time I ever play it, since I rather prefer black's position.

A more open center is ideal for the side with the bishop pair, and the pawn structure is healthier.

However if black lost the center because of this, it would be a bad move.  But his presence in the center is fine.  The pawn on c6 and e5 with the queen add to the d5 and d4 sqaures and black will hold his e5 pawn.

5...Qd4 is more accurate.  

I think he is talking about bxc6, because then Qd4 is not possible. If he IS talking about dxc6, then you are right. 

Good catch.

4...bxc6 is not a blunder per say, but it is not as ideal a move as 4...dxc6.

With 4...bxc6, you weaken the general pawn structure.  The a pawn is forever a liability, if you push the d-pawn at all, then the pawn at c6 will be weak which means you might then have to spend another move to address the weakness, so you lose time compared to 4...dxc6.

Another problem is that 4...bxc6 causes a coordination conflict with the bishops.  The two bishops are immediately ready to develop after dxc6.  But after 4...bxc6, the light square bishop's future is in question.  If you advance the a-pawn to put the bishop at a6, then you lose time.  If you develop to b7, then you lose the advantage of the semi-open b file and have to lose another move by going c5.  If you move the d pawn, then the is a problem with the dark square bishop being blocked in, unless you play for d5.

So is it a losing move?  No, but it entails much more risk to only gain a semi-open b file and centralized pawns.  Not really worth it.

abiogenisis, you apparently have misunderstood.  If 4. Bxc6  bxc6, 5. Nxe5, then what is Black's response?

Your answer, ...Qd4, seems to assume that Black's fouth move was the traditional dxc6.  My question was addressed to the question posed by the OP, namely, what is wrong with 4 ...bxc6?  My suggestion is that one thing wrong with it is that Black cannot play Qd4 after 5. Nxe5.

How does Black fare in that line after 5.  Nxe5? 

i think as one poster already mentioned queen g5 (im bad in imagination but i think that its the correct move) will be the answer

man i lost so often as white in such games, i must be expert on queen d4 and queen g5 moves

Yeah I did, someone already mentioned that.  

Maybe I was misunderstood- I don't think the exchange is "harmless" it's just that black's position is more to my taste.