Why is exchanging the queens bad in this position? Stockfish gives +6.6 to the following position.



The recommended move by stockfish is Rc1 which maintains +6.6 advantage but if I exchange the queens right away (Qxd6), stockfish gives me +5. What's the reason behind the difference (in stockfish points) between two positions?

I can understand by Rc1 we put pressure on c7 but black can exchange the queens and later can defend the pawn too. Also, as a rule of thumb, I don't usually exchange queens off the board if I can take advantage of the position. But here it seems the queens are going to be exchanged anyway.

You can find the full game here.
I think it is because 21.Rfc1 wins the c7 pawn. If black responds with a queen trade, she can't defend the pawn on c7 because white's bishop can attack a defending rook on c8 or d7.

[White "NN"]
[Black "NN"]
[FEN "3r3r/2p1kppp/B2qp3/2Qp4/6b1/PP2P3/3N1PPP/R4RK1 w - - 0 1"]

1. Rfc1 Qxc5 2. Rxc5 Kd7 3. Rac1 {and the pawn falls}


That said, the position is completely winning either way and exchanging off the queens is a practical decision that reduces risks and keeps everything under control. White has an extra piece and a passed pawn.