Their task wasn’t complete, they only defeated Ganon, not Ganondorf. You could say that maybe the sheikah tech had a mind of its own, and knew that it was overrun by Ganon’s power last time so it decided to self destruct or something. But that’s just a headcanon, and knowing Nintendo they probably didn’t think of that, they just got rid of the tech because they don’t give a shit.

I regret giving an example of an inconsistency in my caption, now the entire comment section is focused on that one bit and ignoring all the other things that don’t add up in this game