Looking back at the 1950's and 1960's, remember, everything was made with tubes, except for mainframe computers and exotic aerospace applications. And they weren't all that cheap ... multiply the prices by ten to get a better idea of the real cost.
Tubes are a very small niche market today, orders of magnitude smaller, and if it wasn't for demand from guitarists, there would probably be no tube factories anywhere in the world. As it is, audiophiles piggyback on to the guitar-amp market, and are at least ten times smaller, or maybe twenty times smaller. Fortunately, the middle-class Chinese audio fans are mad about tubes, so there is significant domestic demand in China.
The small demand makes robot automated assembly un-economic, and the R&D budget, compared to the 1950's, just isn't there. It's one thing to have the Department of Defense pay for reliability research, and throw hundreds of top engineers at the problem, and where we sit now, with a only a handful of design engineers worldwide, and none of them with DOD-sized budget.