I have played Bird's opening for around a year now, but I don't understand why Bird's opening isn't played as much as the Dutch, even though it is a tempo up. Why is this?
Even if you play the Dutch a tempo up, you don't have great chances of gaining an advantage (especially if your opponent is completely satisfied with just equalizing). As White you typically want to maximize your chances of getting some edge, and a better way to do this is by controlling more of the centre with 1.e4/1.d4, or perhaps developing a piece with 1.Nf3. The Bird's still a fine opening, but not very challenging.
In addition to this, Black doesn't necessarily have to play 1...d5 (even though it's the most popular move). He could go for something like 1...c5, 2...Nc6, 3...g6, 4...Bg7, 5...e6, etc, playing similar to how he would against the Closed Sicilian. If at any point White decides to push e4, then we've actually got some kind of Closed Sicilian where Black is fine. And if White doesn't push e4, it's kind of odd - after all, in the Bird/Dutch isn't one of the main goals to push e4/...e5?
From my experience in playing the dutch(leningrad and stonewall) and the bird(typically reverse leningrad dutch), I feel its very tough to get an edge but lets people get a levelled game. You also don't really surprise people. Half my games goes something like this f4 d5 Nf3 c5 g3 g6 Bg2 Bg7 O-O Nf6 d3 O-O, and from here white has several options but even in white manages to get e4 in, there doesn't seem to be a path to advantage. You don't get a surprise factor when you reach this position either, since most d4 players have experience in this type of structure against the dutch systems. Another big portion, against the sicilian players, gets something similar to the closed sicilian. And there are of course other legitimate options. The only things going for it is
- unfamiliar to opponents(though as mentioned above, sicilian and d4 players typically comfortable). e4 players may have some problems dealing with this however, as they can't borrow their knowledge from else where.
- from's gambit is bad. Just accept it. Less recommended is to transpose to the king's gambit, but if you know your opponent doesn't have experience in the king's gambit, you could use that to your advantage.