I have this headcanon that the Blue Strings after the Doodle War didn't just disappear
But the connection between them and the heroes was severed.
Like at the cost of your free will and body, you become "fearless" and know what to do in a battle.
Essentially becoming a perfect soldier, yet with no thoughts or idea to think for yourself as someone else is doing that for you.
Wouldn't you feel so lost and numb?
I imagine that whenever the Blue Strings take full control over any person's body, they grow numb for a moment and they're in a bit of a daze.
They don't at first realize they have the Blue String; it takes a while to set in that you have it.
Hence, I headcanon why when we control Portia in the Oasis, she doesn't notice it since it's only for one short fight.
Player essentially has to become a soldier for an up-and-coming war and that must feel terrifying.
They're only a teenager, one that never even wanted to go out and do the Key Hunt yet has to deal with the burdens of having to save a whole person, then a whole island.
I feel like another reason why the Blue Strings disappeared not only because the connection was severed but also because after a war is over...
Why would you need a soldier?
They serve no other purpose, hence why the Blue String dipped after the war, since why would you need to be "fearless" and know everything in battle if there is no important battle?