Every missing episode of every show returned gives us more hope that more Who, more Avengers, more everything will be found. It spreads awareness, it shows people there's hope, and it just might get to the person who thinks "what about grandad's collection of 16mm films - maybe I should talk to someone instead of just throwing them out".
So bring on the Fraggle Rock, the Z Cars, the Horizon, Panorama, Quatermass, let's find it. All of it. Even Topless Darts if need be.
I may never want to watch Fraggle Rock, but someone will. Maybe to judge the cultural importance of it. Someone who's a proper Henson historian, maybe? Or maybe we'll find there's a song in there written by someone yet-to-become-super-famous.
Or maybe just because we shouldn't let our history go. If the destruction of Palmyra by Islamic State horrifies you (and it should), then so should (although on a lesser scale) the loss of Fraggle Rock.
Because it's all our shared cultural heritage, it's all important.
And that's why we look. That's why we care.