why? it's quite straight-forward actually, and just a historical accident basically. the people that popularized Buddhism in the West were academics. it arrived in America by way of scholars of East Asia. the East Asian folk practices are absolutely nothing like what is practiced in the west, and arguably are not particularly Buddhist, but more like folk religions with Buddhist vestments.
the monastic tradition didn't quite make it to the West though because it was subsumed by the academy instead. however, the academy is no monastery and they really do favor theory to the detriment of practice.