Why would someone play the QGD instead of the Slav?

I was looking into learning the Queens gambit declined orthodox line aka. 1.d4...d5 2.c4....e6 but no matter how i look at the QGD lines the slav just makes more sense and looks better than the orthodox (1.d4...d5 2.c4...c6) 

In the slav black can easily develop the light squared bishop, in the queens gambit declined black cant.

In the slav if white exchanges on d5 black can re capture with a flank pawn instead of a precious center pawn. 

BG5 after Nf6 doesnt pin our knight to our queen because i never played e6.

Also, in QGD the development of the black queen is harder than in the slav due to e6 being played.

I just dont understand why the Queens gambit declined is so respected if the slav is just the better version. Comparing french and caro kann to this doesnt apply here because 1. the french saves a tempo on the C pawn break since caro kann takes two moves for c5 and the french is a lot more dynamic than caro but that isnt the case with QGD vs Slav.

Why is QGD considered the classical structures and opening as well?

anyone?

The two are quite different, its like asking why someone prefers to eat apples rather than oranges.

The mainlines of the QGD are more balanced than the slav mainline (dutch variation?). Also some people dont want to allow weaker players to enter the exchange slav against them.

c6 takes away a good square for black's knight.

Also, black often likes to do a pawn break with c5 in these openings, and by playing c6 first you have wasted a move.

A simple answer: 

I'd like to be able to drive a simple stick-shift car well before I even attempt to drive a formula one car.  :)

More nuanced answer:  It really depends on how you can play it / enjoy those types of positions.

In my opinion : The QGD is solid, respectable and contains all the "training" you need to graduate to things like the Slav or Semi-Slav full-time.   

I started playing the Semi-Slav and was thoroughly confused. I went to the Slav and was even more confused.

I finally went to the QGD and started from the basics (Sadler's book as recommended by this forum is a gold mine!) and now the transpositions between Slav/Semi/QGD are starting to make sense and I have a better understanding on the ideas thanks to bootcamp with the QGD.

If Anand can bust out the Lasker Variation to hold his World championship title against Topalov,  it certainly looks like the QGD is not going away any time soon.

Bottom line: If you are not a strong player, respect the QGD and do your time to really study the system ... the ideas are generally easier to grasp than its Slav/Semi-Slav cousins.

I like the QGD. If I want to put my c-pawn someplace, it'll reveal itself as the game progresses.

What do you mean balanced? the example of the dutch variation is kind of an extreme one where i dont know where your going with it.

They dont want to allow the exchange slav because it is so drawish or what?

Balanced, as in neither side has any major imbalances other than the position of the c and e pawn. The dutch variation is the slav mainline, so its not an extreme example.
They dont want to allow the exchange because its very sterile and they will have a harder time out playing people rated a bit below them.

Does someone have an example of how the ideas are easy to grasp?

Yeah and there's no easy way for black to play against the exchange slav variation as white's extra tempo will always give him the more preferable position (If white knows what to do, sadly most class players don't), but in the QGD with 2..e6 there is no symmetrical pawn structures.

helpful

The Slav or the semi-slav are NOT a "better version" of the QGD. It's just a different opening.

It's not true that black can easily develop the lsB in the slav, even if it's still open. Then if white takes on d5 the black player welcomes taking with the e pawn because it enters a Carlsbad structure that will allow him to mount a kingside attack (and to white the minority attack: there's always a flip side to a coin).

thats right

choice

Why ?

I think it is easier to learn and play (if white doesnt switch to the catalan i would  say).

Let's not be so critical of the QGD. 

It has a few disadvantages that you mention: exchange variation allows white an extra central pawn, weaker bishop. 

However, you miss the subtle advantages: in the Slav, 1. black cannot hold d5 and develop his bishop because the bishop move weakens the b-pawn and allows a quick Qb3 (d4 d5 c4 c6 Nf3 Nf6 Nc3 Bf5 cd5 cd5 Qb3 wins 67% of the time for white and the rest of the time it's basically a draw).  So black has to either give his d-pawn away to the c-pawn.  To avoid this, black will have to play the semi-slav and leave the bishop behind, but then the critique against the QGD's bad bishop goes away.  
2. Developing the bishop right away uses up a valuable tempo, and putting a pawn on c6 doesn't pressure white's center (if black goes c5 later, that's another tempo).  It can be frustrating to wait on developing that bishop but it can wait: one can fianchetto it later or pull off e5 and develop it after, so it allows a bit more flexibility in seeing white's setup first before committing. 

I don't think the QGD is something one "graduates" from.  I'm a master, and I play it (along with the Nimzo and the Dutch depending on the game and opponent).  Caruana played it against Carlsen repeatedly, and practically every super GM has used it in a high stakes games.  Additionally, there are ways of avoiding the Carlsbad bad bishop via move order (for example, Kasparov plays d4 d5 c4 e6 Nc3 Be7 and for complicated reasons, if white opts for the exchange variation black can play Bf5 later and have a reverse London Opening... g4 in those lines used to look good but Wesley So recently proved Black is holding his own: https://www.chess.com/games/view/14133031) or e6 instead of Nf6 and go for a Meran or QGD: Cambridge Springs or Orthodox depending on their temperament (e6 allows Bf5 in the case of cxd5 exd5 later too).  Or heck, just play the Carlsbad, even top GM's opt for black there as the open e-file allows for attacking chances or one can Berlin-like shutdown white with it. 

So, do you hate waiting on the bishop?  Choose the Slav.  Do you not need a d-pawn and are okay with a space disadvantage?  Choose a Slav.  Do you want to avoid symmetrical positions?  Choose the QGD.  Do you want to maintain your center and not have to worry about Qb3 tactical shots?  Choose the QGD.  Both are viable for different reasons.      
 

I guess that's that.

What NM alacritous said.

Has chessteenager been here since 2013?