Albumen paper, when it was a commercial product, was just albumenized paper that still had to be sensitized in a silver nitrate bath and dried before using it. After that, it starts turning brown after a day or so. Not having to coat the albumen saves some labor, but it's still not a ready-to-use product like ordinary silver gelatin paper. If someone were to sell sensitized albumen paper, they'd have to make it to order, dry it so it's ready before an available shipping slot, and ship it by whatever the most expensive method available is.