It's
All down to the quality of their education.
One in seven home networks in North America are infected with malware, a recent study has revealed. Half the threats detected during Q3 2012 were made up of spam-spewing zombies or banking Trojans while the remainder were mostly adware and other lesser threats, according to a study by Kindsight Security Labs. The study was …
Massive assumption: the results are accurate and not "45 minutes" sexed-up bullshit.
It's not just the USA, it's everywhere. Computers are like cars, almost everyone uses them but very few understand how they work or are capable of even basic maintenance. The analogy with cars goes even further given than it is increasingly difficult to do work on a car without access to specialist equipment, and in the computer world it is increasingly difficult to replace parts without access to specialist equipment.
The other big issue is the homogeneous nature of most networks. Windows all the way down and suffering all the ills that brings. Although it is interesting how Linux is now being infected (Android is a Linux, remember).
I may be wrong, but I was under the impression that the software being installed here was run centrally by the ISP.
Certainly that's what UK ISPs NTL (big) and Metronet (LITTLE) and maybe others used to do in the days when they each had a separate facility to centrally monitor some customer traffic and put the customer in a "walled garden" till things were sorted out if certain virus-related signs were spotted in their traffic.
'Course that requires ISPs with a bit of a clue, and a bit of motivation, and the UK ISP market is largely dominated by the race for the gutter these days.