The cynical answer is corruption. Military–industrial complex, etc.
this is off-topic, but did you see that article in Businessweek about the bomb detector.
http://www.businessweek.com/articles/2013-07-11/in-iraq-the-...
Ok, that's pretty obviously a fraud. But what it made me start thinking is if you can take an empty plastic handle and a radio antennae and sell millions of dollars of them ... there must be a ton of stuff that doesn't really do what its supposed to but people buy anyway.
This is one of the reasons I make sure I know how everything I own works. That, and the good ol' hacker ethic.