There's a legitimate market for collectibles, and just because we can scoop up an armload of plain red paper luggage tags doesn't mean that some collector in the USA can do so. If they want such an item, then $4 plus postage is a lot cheaper than coming here.
I also see Qantas economy longhaul kits up for auction on eBay, and occasionally they go off.
The business and first class kits are guaranteed sales. They usually go for between $5 and $20 depending on what's inside.
I'm guilty of buying this stuff to some degree. I carry a red leather men's First Class kit in my carryon. I've augmented it quite a bit, and it does double duty as being my inflight amenities kit with better gear than I get in the economy pack, such as lip balm and stuff, and it's also my emergency toilet bag if my baggage is delayed or (more usually) I am between flights and I want to freshen up a bit. The small canister of shave foam is particularly good for this - it's a lot smaller and lighter than anything I can buy in the shops, and beats trying to lather up with the squirty soap in the gents.
Besides, it looks great. That soft red leather bag is really nice. I don't know how much something like that would cost in a specialty luggage shop, but I'm betting it would be closer to fifty dollars than the few dollars I paid for it on eBay.