I suspect that many of the authors who are auto-DRMing their books are simply letting their insecurity and possible paranoia and ignorance allow them to be sold snake oil, as
this thread in the Workshop forum would seem to indicate.
Protip for aspiring authors: much of the time, no one's going to bother to pirate your book because they've likely never heard of you enough to consider your book worth taking the time to pirate.
Piracy means that at some point, someone actually cared, and if they cared enough, then DRM has done absolutely nothing to prevent them from spreading that care throughout the intarwebs.
<-- The dancing lock icon mocks you with its "I'm goofing off and not working when you thought I would be working" dance of mockery.