The Blu-ray format doesn't encode freeform metadata into the stream. The idea is that it would be on the menus, so there's no need. But on a menuless disc, well...
There is actually some limited metadata. You've got language, which the player will show, and you've got type of audio encoding and number of channels (derived from the actual audio track, you can't set this), which they player may or may not show, but that's about it. No dates, no general-purpose text comments field.