Headline's a bit misleading. They've never permanently lost a bag, and well done to them for that, but they've certainly lost them for periods of time. Just eventually found them.
Permanent losses are pretty uncommon in general. Good for them for minimizing but having bags on the next flight or delayed for a couple/three days is way more common. Probably would have to be stolen which is rare, especially in Japan, I assume or end up in some weird location without a scan.
Was flying into Narita once and I had checked luggage in part because I was carrying an award for a Japanese customer. I was sort of given a "we'll get back to you sooner or later." At which point I explained the situation to a supervisor I think and was much fluttering around and got the bag the next day.
I honestly have no idea how those dynamics work. At some point, the airline presumably pays, travel insurance does, or a combination of the two. At some point if it's just a bunch of old travel stuff, I guess I can see a customer shrugging, collecting the money, and dropping the whole thing.
I'm now imagining a situation in which a customer at the point of successfully making an insurance claim to pay for the nice new clothes they've bought themselves is infuriated to receive an email informing them that Kansai airport has found their luggage and will endeavour to deliver it to a hotel anywhere within the world within two days...
The customer has presumably been paid. If they're smart there's nothing or very little in the suitcase that can't just be replaced. The airline/insurance has paid out and just wants the claim to go away.
As a side-note, had a small kitchen fire with smoke damage last year and it was pretty obvious that, even though they were reasonably generous, the insurance adjuster, cleaning people, movers, etc. just wanted the whole process to go away so they could move on. They objected a bit to a few claims but, for the most part, spending $50K was nothing compared to the claims being reopened.
Once the insurance adjuster is satisfied that you're not scamming them, they're often quite flexible and lenient.
I've only ever had luggage delayed once, they gave me a little bag of toiletries and a couple hundred bucks and a few days later delivered the luggage; never demanded the money back.
And that's not a permanent loss. It may screw up your trip to a greater or lesser degree but I try to build in buffers at least for a shorter delay when I can. I have also had a few multi-day delays--on of which just caught my guided hiking trip with like an hour to spare. And I had already bought a new duffle bag worth of stuff as best I could.
Was flying into Narita once and I had checked luggage in part because I was carrying an award for a Japanese customer. I was sort of given a "we'll get back to you sooner or later." At which point I explained the situation to a supervisor I think and was much fluttering around and got the bag the next day.