Why are u not able to answer a simple question here?
Are US players allowed or not? Why is nitrogen not able to say that publicly when all other books do it
Because they know it's illegal for US players to place bets, but it represents most of their consumer base (just look at their marketing/promos - you can tell it's tailored towards the US market). So, they say "play here at your own risk, up to you to decide whether it's legal in your jurisdiction" because they know that many players can't resist.