Why does black have an advantage here? I am studying now old Polish book &quot;ABC Szachisty&quot; (&quot;ABC for Chess Player&quot;, informal translation) and the following example is given there:


[FEN ""]

1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. Nf3 e5
5. d3 Bg4 6. Bd2 Nc6 7. Qe2 Nd4 8. Qxe5+ Qxe5+
9. Nxe5 Nxc2# 


And this example is aimed to show the significance of the center. So my two questions that I don't understand here are:

Why this example satisfy its aim, i.e. shows how important the center is? My guess would be that since black figures are well centralised, they have short distance to white's position, and that is what is making mating attack possible (also white's mistake of taking the pawn). I don't understand however why control over the center is important here.

Why, after 6th move black has better control over the center?




[FEN "r3kbnr/ppp2ppp/2n5/q3p3/6b1/2NP1N2/PPPB1PPP/R2QKB1R w KQkq - 3 7"]


I see that white knight on f3 is pinned and f1 bishop is blocked. Also, white game is very passive here. However, black has only two minor pieces mobilised here and whole queen's side is not active.
First things first, this is an example of a very poorly played game, so Black gained its edge because of White's tactical mistakes, rather than by taking advantage of their extra space. This is a &quot;fault&quot; often made by chess authors when trying to illustrate a concept. They will explain the events in a game in a way that &quot;fits their narrative&quot; rather than provide an objective analysis, which is this case would lead to conclude that the position is pretty much balanced if not slightly advantageous for White until the horrible 7.Qe2.
It is true, though, that by move 6, White's lack of interest in fighting for the center costed them most of its starting advantage despite Black having lost several tempi with their queen. White could have played 7.Be2 (among others) and still have a reasonable position despite Black's lead in the center due to their extra development.