[Legends: Arceus] Sea's Legend quest: How are you supposed to know what to do?

Edit!:

[If you're looking for how to actually complete it, just search for one of the many wal kthroughs, but I won't go into it here to avoid spoilers]

Apparently the way you're "supposed" to figure it out is by having bought and played Brilliant Diamond and Shining Pearl, read a book also called "The Sea's Legend" from a random bookshelf, and it gives you the instructions for what to do.

Now, since I can't delete this post, I guess I can change it to a discussion prompt XD

Why would they make a quest that's so intentionally obscure and frustrating like this? Keep in mind that you need this quest to complete the game and catch Arceus. And yet there is not only no way to legitimately complete the game without having also stumbled upon a book in a completely different game, but also no indication that you should be searching in that game instead of this one—and even if you have completed Brilliant Diamond or Shining Pearl already, there's still no hint that you're supposed to go find a book on a bookshelf in order to complete Legends: Arceus. Are they trying to intentionally waste the less Google-inclined fans' time?

Luckily, I had already broken and Googled the locations for the remaining Unown (I was dumb and didn't realize there were in-game hints for their locations XD), so I was relatively quick to break when trying to figure out this quest as well.



Original Post:
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[[To be clear, I already know that there are guides for what to do, and I already know what some of the steps are.

How, in-game, are you supposed to be able to figure out what to do? It seemingly just mentions "East Sea" and "Princely Pokémon" and then completely throws you on your own to "Find the mysterious Pokémon". A lot of the steps involved are incredibly specific, so how in the world would a player who doesn't want to seek help online figure out what they're supposed to do? Is there something I'm missing? Or is the point of this quest to get people to ask about it from other people?]]
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I think it is supposed to be for those who have read the books in BDSP Games. In the Library of the 5th gym town, the book was there. This seemed to be a call back to the book that was in the original Diamond and Pearl games that hinted at Zorua and Zoroark.

The creators of the Pokemon Game, tends to throw in very obscure hints about future generations that you would have no idea what it was hinting at until the next game came out. This seems to be one of those moments where they are rewarding the people who got both games. Similar to how we used to only be able to get Manaphy in the original DP games if we got a Pokemon Ranger game and finished the story. Or how we got a Jirachi for RSE if we complete Pokemon Colosseum. So this isn't really anything new from what they've done in the past.

Neat to see it does have precedent—this does seem to be a lot more tame compared to that, considering once the events were over you literally could not obtain the Pokémon, whereas in this game you can simply Google what to do and still get it at any time. Still a bit strange, but an improvement to be sure.

Well this is also another of sales tactic, so you'll purchase all the games they pushed out?
Shaymin and Darkrai will never be in the game if you didn't have SwSh and BDSP as well.
With the close release of BDSP and PLA, some players who aren't that deep into playing Pokémon will make a choice in between the two games and just get either one.
Can't deny that with that, even the least-expecting-to-buy-BDSP (Or PLA) people might even get curious and get it for the sake of finding more hidden Easter eggs on their own, even if they read it online, some will want to "read it for themselves" in their own games, a form of OCD some people tend to have (I know i'll definitely do it too, going by how I had played sequels of games outside of Pokémon before the first and going back to buy the first one to catch up purely because I love the game and wanted to know more about what they're saying in the sequel.). Even if only 0.0001% of the population does this, it is still a win-win situation for the company themselves.