The assumption that there is a lot of tax revenue in poker is problematic. For example: In 2007 the height of the poker boom, the estimated gross revenue from online poker was 3.2 billion U.S. dollars. Let's assume a high tax rate of 30%. That's 900 million dollars. Barely a blip on the tax revenue of many states (CA for example is 112 billion).
Regarding organized "Underground" games, grinders have long complained about those games because they can't get into them, and when accessible the rake is very high. If by "underground" you mean "Home" games; those have always been the backbone of poker in the U.S.
Cheers!