The point is not that you can't find them, but that you are less likely to be able to reliably filter and hire only people that are loyalists and will remain loyalists in the face of learning what the agencies actually do, including when you're placed in situations where you might incite reduced loyalty such as when firing people.
Not only might they be facing a less loyal generation as your pool to hire from, but they can also expect to hire much more than they did a generation or two ago:
These services have grown, and the average time people will stay employed there has nosedived, and the usage of short term contractors have skyrocketed
Given that, it is not unreasonable to believe that the odds of slipping up and hiring the wrong people is rapidly rising, and also that the number of events that are high risk to maintaining loyalty, such as people feeling they are passed over for promotions or raises, or firings or other personell issues will go through the roof simply due to the increased number of people involved.
Not only might they be facing a less loyal generation as your pool to hire from, but they can also expect to hire much more than they did a generation or two ago:
These services have grown, and the average time people will stay employed there has nosedived, and the usage of short term contractors have skyrocketed
Given that, it is not unreasonable to believe that the odds of slipping up and hiring the wrong people is rapidly rising, and also that the number of events that are high risk to maintaining loyalty, such as people feeling they are passed over for promotions or raises, or firings or other personell issues will go through the roof simply due to the increased number of people involved.