If you attempted ‘poly’ a thousand folks a year...say twice each year...you’d have one-third of them on suspension until further investigation could be accomplished. Man-days lost? Probably minimum of sixty days lost on each person with the bulk of the investigations turning up nothing.
In the old days, if you’d just done a financial check once a year....you would have ratted out the bulk of all spies. Today, there are almost no spies...just leakers, where there is no financial gain involved.
This enormous belief that poly is the golden ticket and will find all the problems...it just simply leads onto accusations and enormous security investigations that rarely ever show any payback.
I once knew a person who had their security clearance yanked based on concerns over their financial stability. The person was a valuable asset to the organization and an unquestioned patriot, but they were really serious about security investigations back in those days. Not so much now.