Studios have realized that releasing a documentary about how a show was made is a marketing strategy. The Last of Us podcast and the Lord of the Rings behind-the-scenes reels are technically entertainment industry documentaries—they just happen to be funded by the same studio whose film they are covering.
A brilliant example of the "failed production" doc. Jon Schnepp investigates the infamous Tim Burton/Nicolas Cage Superman movie that never was. It reveals how studio notes, changing management, and creative chaos killed a $50 million project before a frame was shot.