Why is KuCoin illegal in US?

Could you possibly explain to me the reasons why KuCoin is considered illegal in the United States? I'm particularly interested in understanding the legal frameworks and regulatory issues that lead to this conclusion. Is it because of the nature of the cryptocurrencies traded on the platform? Or is it due to KuCoin's operations and business practices that violate US laws? I'd appreciate it if you could elaborate on the specific laws or regulations that KuCoin violates in the US context. Thank you for your insights and clarification on this matter.