It probably affected a few thousand people I’m guessing, not everyone. Not all accounts got affected and those that got affected weren’t all affected in the same way. Those who noticed most were probably those with personal storage guilds, as for those, only one or a few people interacted with the bank, so it was easier to tell if something was awry. With a normal guild bank, especially at the very end of an expansion, a lot of things might be happening with many people involved, so it’s harder to tell. My one bank had about 98% of the items lost. Another had maybe about 30 to 40% lost. I’ve felt it especially now, trying to craft some Enchanting Housing items and I KNOW I had a ton of it before, but now have to go farm for it, at a time when there’s LOT I have to get done in and out of the game.
If you want a good explanation, go watch Kurnmogh’s video “The Great Blizzard Bank Heist.” She made several but just watching the first will explain it well. She was a member of what some of us began calling “The Maw,” the Forum Threads discussing the issue at great length. (Full name of the threads: “Guild bank missing items - what happened?,” and “Guild Bank Missing Items Bug – Aug/Sept 2024 (Part 1)” and there is a shorter, part 2 as that one reached its limit, where Linxy, a Blue, tries to explain (though not well - not his fault. He’s just the messenger trying to explain what should never have happened) that they are going to do a PARTIAL restoration (which turned out to be EXTREMELY LITTLE to NONE for most of us). I doubt you’re interested in reading those though (in fact, I’d be surprised if you made it this far in my post).
It didn’t make much news on the larger 3rd party sites, outside of a few here and there, and often, they were reporting “the official” word, rather than the real experience. (From what Blizzard said, it SOUNDS like a lot of people got a lot of stuff restored when that was nowhere near the case). I think, IF this was an honest mistake, there were too many accounts for them to want to take the time and resource to do manual restoration and yet, too little for it to make BIG NEWS where they’d feel compelled to act. Though now, with all of those old mats being needed, I have a nagging feeling maybe it was a CONVENIENT error.