It scores so well for black because alot of white players don't know what they're doing and weaken their dark squares by playing e4 (and/or Bg5xf6), and then castle kingside straight into black's attack.
Also, it is mostly reached through a 1...Nc6 move order, and most people who play it likely specialize in these structures, which could explain black's score.
After Ng6, black wants to play Bc5, Nf6, d6, 0-0 and play for a kingside attack.
Something like this:
having just started playing the englund gambit > hartlaub charlick variation 1.d4 e5!? 2.dxe5 d6 3.exd6 Bxd6, I need something to play against 2.c4. My instinct (and because I always wanted to play it to begin with) would be to play 2...d5 and transpose to the albin counter gambit, but it has terrible stats.
2...Nc6 3.d5 Nce7, on the other hand, has KILLER stats as UGLY (as in stonewallish straightjacket with pawns in the way in the center and a poorly placed knight) as it looks to me.
what's going on here? what is black's positional edge or his powerful plan to get such 41:56 stats in EITHER main line?
and black plays ...Ng6 after EITHER 4.Nc3 or 4.e4 and at least in the 4.e3 line, gets AT LEAST a 56% win rate no matter WHAT line he choses to play! there's some powerful mojo happening here.
i look at it, and I see a hideous closed center I'd want to sack a minor piece if I have to to open things up.