Lagers are easy drinking and have been highly marketed in the US. After prohibition killed most breweries, consolidation led to Bud/Miller/Coors dominating the market place, and it's only since about 1980 that there's been an expansion of craft breweries. Those tend to be fairly split--Sam Adams' biggest product is their Boston Lager, but Sierra Nevada's is their Pale Ale.
Beer in the United States - Wikipedia, the free encyclopedia
Here's a good read on the subject. Also think that after prohibition while a lot of men were at war and the big breweries were trying to get going again that it was the women who were mostly home to drink it and how many of them do you know that really like a nice IPA?