i didn't go to the BLS to see the age groups, but at least on the west coast, virutally every kid plays/played youth soccer. maybe that skews it. baseball and football were much more for kids whose families had an actual interest in them being involved in athletics. soccer was just sort of a norm.

as an adult, i don't know any adult who plays any team sports except pick-up basketball at the park, and this is a group of probably 20 relatively fit/healthy 40 something guys. many skiers. MANY golfers :|. a few cyclists. no football, no baseball, no soccer (actually maybe one now that i think about it), no volleyball. just not practical.

cycling, running, walking have the beauty of being sports that don't require a court/field. it's great.