Why is 1. d4 2. c4 3. b3 so bad for white?

Question

I recently played a game that opened like this:

1. d4 c6 2. c4 d5 { D10 Slav Defense } 3. b3
[FEN ""]

My third move, 3. b3 is apparently so uncommon that Lichess doesn't have it in its top 12 most common moves.

Stockfish rates the position after 2 moves at +0.2 and after 3. b3 at +0.0, so it's theoretically not terrible. However, the top 6 responses for black (topped by 3..Nf6 and 3..3Bf5) all have winning percentages favouring black (39%/54% for the knight), so there's clearly something wrong with it.

I often feel intuitively that I want to make this move (and in similar positions), reasoning that I prefer to bring my pawns towards the centre. Pawns on c4 and d4 look good, although I imagine b2 can become vulnerable.

OTOH, I can see that this move doesn't help develop any pieces, and maybe white is now going to be a move behind black after something like 3..Nf6?

I'd love some explanation about why this move is so dispreferred.

Answer 1

Stockfish evaluation is not the only criterion to determine whether a move is sound or not. The main issue with committing so early to 3.b3 (against this particular Black setup) is that there are no downsides to delaying that move.

In other words, even if you want to play some setup with b3, there's no reason do it right now. Instead, other moves that prioritize development like Nf3 should go first.

Anyway, just because a move isn't popular, it doesn't mean it's "bad". It just means people prefer something else. Think for instance of 1.Nc3, a move that is hardly ever played. Is it "bad"? Not really. There are worse moves that get played more often. The reason 1.Nc3 is so rarely played is that there are more "comfortable" move orders from which you can get the positions that arise from 1.Nc3

Answer 2

There are 3 main reasons for this move to be inaccurate.

1. It doesn't place any pressure on black's position.
2. It weakens c3, allowing black to "force" your knight to the more passive square d2.
3. It removes the Qb3 move, which punishes the early development of black's LSB.

All of these allows black to develop more easily and equalize.

Answer 3

One should be very careful with the win percentage parameter. Probably here b3 was mostly played by lower-rated players trying to avoid theoretical lines and confuse the higher-rated opponent. Another example of the same fallacy: I don't remember losing in the exchange french with black. Of course, it's not because 3. exd5 exd5 is so great for black, it was just played vs me mostly by lower-rated opponents hoping for an easy draw.

Your 3. b3 will likely transpose to an anti-Meran-ish structure if black does not react immediately (for example, dc bc e5 might be worth looking at). Also, good point by @Mike_Jones about Bf5 or Bg4 which is often met by Qb3 in the Slav.