… except, conveniently, for the Guardian parts used in the Skyview Towers (the “arms” that grab Link, the control units, etc.), or the dead Guardian atop the Hateno Tech Lab, or the Guardian “daggers” that were formerly turned into Ancient Arrows (which Link can DIY now), or the Purah Pad which is basically a rebranded Sheikah Slate, or the telescope atop Purah’s little lab at Lookout Landing …
Oh and of course the after-credits scene in BotW, where Zelda states that she wants to go investigate Vah Ruta to find out why the Divine Beast stopped working and check whether it can be repaired. The “Calamity” was dead by then as the scene takes place days or even weeks after the final battle, but I guess noone had told the Divine Beasts yet that they were meant to inexplicably go poof along with the main antagonist.
IMHO it would have made a lot more sense to say that the people of Hyrule actively dismantled and destroyed most Sheikah Tech they could find so it would be impossible for Ganon to possess them again. That would explain why there is still some of it left in remote corners of the Kingdom, and it is a more down-to-earth explanation than “it just vanished”.
All in all, it really DOES sound like a lazy “I don’t care” explanation.