Why isn't Bird's Opening at least as popular as the Dutch Defence? The Dutch Defence is a fairly popular response to 1. d4. So shouldn't 1. f4 (Bird's opening), viewed as a Dutch plus a tempo, be at least as popular?
A good opening for Black seldom is a great choice for White even with a tempo up. Grandmaster Alex Yermolinsky discusses reasons for this in his book "The Road to Chess Improvement". One of the main reasons is that the opening goals are not the same for both sides in the opening, and schemes that are suitable for defense or counterattack are much less valuable for assuming the initiative.

Famously, when grandmaster Vladimir Malaniuk, a great proponent of the Dutch Leningrad with Black, had some issues with his White repertoire, someone suggested to him that he should start with 1.f4. His retort was definitive:


  That extra move's gonna' hurt me!


As a side note, the Dutch is not that popular, especially at the highest level.