Aside from the state run lotteries, and Las Vega etc., the largest lobbying group in the US associated with gambling probably consists mostly of "Tribal Gambling."
Most of the states have had anti-gambling laws for decades, and the "Independent Nations" of Native Americans provided an out to allow casinos and bingo parlors "on foreign soil" right in the middle of the US - without state politicos having to face up to whether it was something large numbers of people wanted.
The Tribal casinos have been a very effective barrier to legalized gambling of all kinds in many of the states. They contribute heavily to buying the appropriately connected politicians, via their lobbyists and PACs, and are extremely protective of their "exclusive offerings."
Any attempt to enforce existing laws and/or to shut down internet gambling most likely comes from existing gambling operators in the US, and largely is a matter of who pays the politicians best.
Recent attempts to approve "Indian casinos" in Kansas have been stonewalled by opposition from the "Indian casinos" in Missouri and Oklahoma, and it has been impossible (or simply not necessary), thus far, for Kansas to offer citizens a chance to participate in the debate.