One: the perception in the legal establishment is that firearms are a deadly tool of mass destruction which cannot be entrusted to Joe and Jane Citizen without extensive public oversight.
Two: those 300 million lawful guns are concentrated demographically among a small number of people compared to the entire US population. One guy in ten owns half of Cabela's SKU inventory f from .22LR all the way up to .50 BMG while the other nine people are either totally gun-less or own one pistol collecting dust under the kitchen sink.
Three: gun owners are no more politically savvy or active then the general population. At the range it's all talk about action and involvement, but crickets when the time comes to actually vote and participate in the political process.
Ultimately what we have is a basic public relations problem. Most of the world's movers and shakers in government, business, and media entertainment collectively believe firearms are a social ill comparable with inbreeding and meth-lab trailer parks. We need to lift the curtain on the social benefits firearms offer. Catch is someone's going to have to start a media conglomerate from scratch to do it, because the current ones have an institutional bias against guns that runs deeper then Saudi Arabia's aversion to gay marriage.