One man’s quest to revive the great American vacuum tube
My guess is that people are buying tubes because of the impression that they are rare and hard to get, and owning one is a privilege, which makes people accept a high price.  If a domestic factory starts cranking out tubes, even with a similarly high price, the <i>impression</i> of rarity and unavailability won’t be there, and I suspect that people then won’t buy them.