Discovering and using private APIs is not a walk in the park. I doubt "laziness" is a common motivation for doing so. Lack of knowledge or bad docs, perhaps. But there's often no officially sanctioned way to do something that people want (and perhaps will pay for) - most private API usage I've seen falls into this third bucket.

Laziness comes in many forms. Arguably, discovering and using private APIs is a form of intellectual laziness — it requires you to refuse acknowledging that the whole system is telling not to do things that way.