Is this anything more than just supply and demand? As a society, we have shunned physical labour as an effective means to earn a living. In the education system, we insist that everyone graduate from high school, regardless of the attained level of achievement.
As a result, we have a huge supply of young people who are college educated and have eschewed the trades because they believe that physical labour is below their standing. They're not wrong, since that's what they've been told their entire lives. They're all looking for white-collar work, but we simply don't have enough jobs for all of them.