What contributes to Anheuser-Busch having 50% market share?

Hi,

I'm interested in what policies and regulations for beer and alcohol give the big breweries like Anheuser-Busch such a huge market share. Quality wise, their beer doesn't compare to micro-breweries. Is it just that most Americans like bland beer, or do beer regulations make it more difficult for micro-breweries to compete? How?

If you could create an ideal beer market where there was diversity and the little guy with the highest quality was a serious threat to Anheuser-Busch, what would the perfect regulations look like?