I suspect they stopped bothering with optional rooms because their data showed that most groups were skipping them.
Haukke Manor HM is the best example I can think of. There's an optional room at the end that has two equipment containing treasure chests. It's not guarded by enemies so it's basically free company seals.
I haven't seen a group for for those chests in years. Whenever I go to the dungeon I run back and grab them once everyone else has left.