1. The original ten tribes weren’t all that lost (and most survivors probably joined up with exiles from the other tribes a few years later).
2. Most of the “lost Jews” people keep discovering are from the mainstream tribes who didn’t start getting misplaced until the end of the Bayis Sheini period.
3. People like discovering interesting and lost lost relations.
4. Many Jews have a legitimate fear of getting lost, so its nice to hear about finding some who were lost and now are found.