Why shouldn't I play c5 in Queen's Gambit Declined as white? My favorite opening is the Queen's Gambit Declined, and I will often reach positions like this
[FEN &quot;&quot;]
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. e3 c6 5. Nc3 Be7 6. Bd2 O-O 7. c5

Where I decide to play c5 after my rook is safe. If black goes after the c5 pawn with their pawns then I defend it with mine, and when I run this with Stockfish the pawn is indeed not captured.
The thing is, this move is generally always classified as an &quot;inaccuracy&quot; or &quot;good move&quot;, but never as &quot;excellent&quot; or &quot;best&quot;. To me, it feels like this move severely cramps black's dark-squared bishop as well as just gaining me a lot of space and control on the Queen's side.

In general, why is playing c5 as white in the Queen's Gambit Declined not a good idea? As black, how should I go about defending against this move?
In most cases White doesn't want to play c5 in such positions because it takes the pressure of the black center. Yes, it cramps the black queen side a bit but it allows Black to play e5 at some point and break the center instead, freeing their c8 bishop and more. With the white pawn on c4 that is more difficult, sometimes d5 may just be hanging after e5 and even if not White can take on e5 and d5 to give Black an isolated queens pawn with not much compensation. After c5 Black has no such problems and can freely play e5, banking on a well defended d5. If anything it is White then who has to be careful, the d4 might become slightly weak, or after a capture on e5 the c5 might get into trouble later.
Of course as with everything it depends on the position. E.g. if Black already committed to a6 like in a Chebanenko Slav then c5 may be a good move as then b6 really is quite weak.
(also I should give a disclaimer that I'm not a d4 player so take this with a grain of salt)