It's because of their short attention span. Really, every popular sport in the US have a lot of interruptions to go and get a snack or show commercials or something. (American Football, Hockey etc.)
Basketball is probably the 2nd most popular sport in the US and while it's not as fast paced as soccer, it's pretty continuous. I doubt attention span has anything to do with it, soccer to most people here is just boring, why do people get offended when Americans say that?
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