This has been explained over and over again on FB, this forum, and who knows where
, but the bottom line is: POTF is a relatively small independent band. They can't exactly choose where to play. You can easily calculate how much it costs to fly 10 people + instruments and other equipment to the US, plus accommodation etc. You need to get at least that much from ticket sales (in practice much much more since there are so many parties who take their slice), which means you need to get at least a thousand or so people to buy a ticket.
Outside Finland, there are already a few countries where this can happen (Russia & India for example), but unfortunately US isn't one of them, yet. In practice, an organizer or venue in the US must negotiate a deal with POTF's booking agency, and so far, that hasn't happened. The band needs much more exposure in the US before any organizers get interested. On the other hand, as soon as that happens, the band will be on their way to the US at that very moment.
Meanwhile, you can spread the word to your friends, contact local radio stations etc. There's also an excellent POTF US Street Team on Facebook, who have already done a lot of guerrilla marketing in the US.