Then how do you explain the high unemployment rates? If this need was so great then would not the unemployment rate be close to nill?
Because I don't think unemployed IT workers and financial analysts are rushing to go roof houses. Do you? They are still unemployed yet those houses still need roofing.
And fwiw, our unemployment rate is not high. Historically, it's actually very low, and fell dramatically throughout the 1990s, during this deadly "Invasion". (You'll notice the chart is rolling over, making an identical pattern to previous economic cycles.)