The only conclusion I can come to is that DRM does work (for some definition of "work").

This isn't a poorly-studied field. Piracy rates have been carefully tracked by every major publisher for years but the information is rarely made public. Ubisoft has experimented with several DRM methods in the past, including having no DRM at all on 2008's Prince of Persia.

I figure that someone's come to the conclusion that using DRM makes more profit than not using it. And also those at every other major publishing house after studying their own figures.