A more-logical explanation is the relatively-anitseptic nature of most of the items in modern American life, especially with the chil'run. With the relatively-harmless bacteria being systematically wiped out with various antibiotics (especially soaps, which came on the market in the late '90s), that leaves the much-harder-to-kill viruses (and those bacteria that survive the urge to purge) to attack an immune system not stimulated by the presence of the harmless stuff.
Exactly! The envirowackos will try to find any excuse to avoid admitting that we need to start spraying DDT.