I wonder if anyone has run the numbers on what the actual cost, both in cash and logistical headache, contacting so many copyright holders would be. That seems like quite the feat to calculate.
Doesn't really matter. The incentive structure to steal clearly exists, so why would they even go through the trouble?
There's an established network of intermediaries that can supply a large variety of books for a few dollars apiece, so no need to contact copyright holders directly.