There are some extra hoops that online betting sites must jump through in order to legally service the United States gambling market. It is a hefty investment and a lot of work to offer US-friendly online gambling, and not all brands are in a position to meet the standards necessary for success.  Gambling-related financial transactions for US gamblers must be done using only reputable, US-friendly funding options that utilize reliable payment processors in order to operate successfully within the confines of the UIGEA, and only the most established and committed gambling sites are going to be able to pull that off. For many less popular sites, its just easier to stay out of the US market altogether.