Yes and no. Probably because of the restrictions of crypto currencies in the US. That is why a lot of ICOs do not let US citizens to participate in their ICOs. Unfair it is, but that's just how things work. Nothing we can do about that.
But there are also a lot that accepts US citizens but there really aren't a lot that I have seen. But anyways, i wish this changes soon because a lot of US citizens are really into crypto currencies. This would really be great for the crypto world.