Supposing you're right, I can think of some reasons:

apples have spread from Kazakhstan in their thousands of varieties adapted to climates from cool to frigid (the original liked the slopes of a breezy river valley.)

So since the colonies in North America, you could easily have an apple grove. If you were fancy, you bought imported cultivars from Stark Bros, see Thos Jefferson.

In the United States, the #1 beverage until Coca-Cola was apple cider. Lots of factors there.

It's kinda like saying "why is France so focused on wine?" Or California! But if you go to California, it's apricots, almonds, peaches plums pears persimmon blackberry blueberry boysenberry which have all got shorter shelf-life and season.