Yes, they're far more common. I don't recall seeing oat milk on store shelves until very recently.

According to a source, "almond (64 percent market share), soy (13 percent market share) and coconut (12 percent market share)"

http://www.mintel.com/press-centre/food-and-drink/us-non-dai...

EDIT: I should add, for those interested, that this dominance is perhaps less strange when noting that California alone produces around 80% of the world's almonds.