It's an interesting hypothesis and maybe there is a little truth in it, but ultimately I think Eric Peters has this one wrong-- or at least as it pertains to my home state of Minnesota.

Where I live, adults frequently cycle to virtue signal that they are on the "green" team: the alien-head helmets and tight clothing are their side's uniform. And they deliberately ride on the roads just to slow down car traffic, even in the presence of massively wide, often-times even lane-marked "sidewalks" running alongside the car street. These "sidewalks", which are more like miniature bicycle roads, are so large that they force the car roads to get cut-down to one lane each direction, further discouraging driving.

Another give-away is how militant and aggressive are many of these adult bicyclists to car drivers, for basically any excuse. Imagine "road rage", complete with shouting and the flipping of the bird, but while riding a bicycle.