The answer to the question. Why does the Massage quest not to progress. It is blocked by the Helping Hand Quest.
If you played BB, you should know that there are end-to-end quests. This means that any quest is not completed and may continue with the release of a new update for the game.
DS makes mistakes in the game code, and because of this, problems arise in the game's quests. If you make a separate render for each action of the main character, the game will weigh not 1G, but 10G, so you have to endure such restrictions in the game.
not sure about that helping hand thing, I think on my playthough (no previous hacks or anything), everything was waiting on that massage thing, there was nothing else to do, and Julia simply didn't show up at 16:00, I can't recall exact things I tried, skipping a day, trying next week or something like that, nothing helped, the "fix" fixed it immediately, and a quest or two later the script again didn't want to proceed, switched back to original game files - problem solved, I haven't finished all current content yet, so can't say if this "fix" broke something else or not, what I remember doing - I think there were 3 of those events in that quest, and I tried reverting back to original files after the first event thinking just the first trigger is broken, but Julia was a no-show again with the original files, so had to use the fix for that whole quest
I am aware of how bb or any other of these "in development" games work, and only the terribad ones have no messages when you reached the end of a quest in current version, if the quest has ended - all requirements finished - it should be marked as such regardless if that is the last thing in the patch or it will continue 6 months from now, and this clearly is a quest description mistake to not mention the shower scene, the walkthrough was what helped me, there should be no need for walkthrougs if the questlog was in order, this game has a pretty decent one though, not too revealing
and a unique 15kb icon for each quest wouldn't balloon the game size like you suggest
edit: one thing I just noticed about what may have caused the Massage event not to trigger, selfies for Angela at the principals office, I never did finish that one completely, I made a few and then her final test triggered, which then marked that quest as finished, so I didn't bother with the rest of selfies for other class mates, perhaps that may have caused the Massage-Julia-16:00-no-show issue, but CBA to replay to test it