[schrototo]

Neither of the articles you link to say that unionisation is the reason for the ongoing shift to contract work, or even mention unions at all...

If anything, (stronger) unions are exactly what contract workers need.

What caused the shift to contract work? Greed. Greedy employers who don't want to give up the tiniest bit of profit to pay for living wages, health benefits, retirement plans or workplace safety, and then have the gall to re-brand deregulation as freedom.