Here's the thing, and I know it's not a popular opinion but it's the best way to do things. Future content, no matter how far in the future, is always sprinkled about when we update for a very specific reason.
In Zelda you're in a static world. It doesn't grow, it doesn't change aside from prescripted events. What you see when you first enter the world is what you'll see when you beat the game. So given Zelda's progression, it's easy to have secrets and items already there so you can make a mental note and remember to return later with new items that will let you access that content.
But Graal doesn't get that luxury. Classic is an ever changing world, where things are always being added. So that introduces a problem that Zelda doesn't have. If we add all the appropriate content when a new item or quest is added then it spoils most of the surprise and doesn't give you that satisfaction of remembering things you've seen as you played. If we added a new quest and all the NPCs needed to complete it at the same time then you're no longer looking for NPCs that fit the description of the quest you're on, but new NPCs that you haven't seen before.
This is why things like the abandoned house in Onnet were added long before Destiny, even though it was part of the Destiny release much later. So when you finally did get to go into Destiny and start that quest, you wouldn't immediately think "Oh ya, that's easy it's the new house that appeared in Onnet at the same time!" You'd have to actually think and apply your knowledge of the world to finish the quest. The downside is sometimes content that was planned is pushed aside because of priorities or change in plans, and sometimes those plans are abandoned altogether. When that happens it leaves content that was preemptively added for said reasons being left in the world with no actual plans to be used.