Various crooked reasons. Some common ones include:
1. Covering incompetence. Poor sales of bad product are blamed on pirates, and those who were responsible can say "but we don't sit idle, we put another DRM in place".
2. Control over the market (standards poisoning, excluding competition, lock-in and etc.). That's what mobile carriers did to prevent people from switching to competitors.
3. Satisfying their hunger for power and ability to tell others what to do or not to do. DRM allows creating new "laws" without any democratic process. As soon as something has DRM attached to it, they can forbid what they don't like using DMCA-1201.
And so on and so forth. Those who use DRM know perfectly well that not only it can't reduce lost sales, it only increases them. So they use it for very different (and crooked) reasons, unless they are simply completely clueless.
Wasn't its DRM broken? They always are. Some observe, that the mere presence of DRM is an incentive for some to break it, since they see it as a sport.
