Why Can't Tubes Be Mass-Produced Cheaply?


I often read that old tubes manufactured from the 60's or earlier are collectible items and often much sought after, and new tubes are not as valuable. Reasons cited are that these older tubes are a rare species, and they often sound 'better' and hence the hefty price tag on them. I am puzzled as to how these older tubes are different from the new ones and why they are better-sounding. Why can't technology today produce tubes that are similiar in quality to those in the yesteryears, or even better them? After all vacuum tubes, electron tubes or valve tube(where they call it in Britain) are electronic components made up by plates and filament. What happens if these old tubes become extinct? Why are there still so many of these old tubes available for sale although it has been almost 4 decades since they were manufactured? I mean once these tubes have run out of life they will basically be disposed off.

Pardon my ignorance as I cannot seem to find any discussion on this matter elsewhere. Any opinions would be much appreciated.
ryder
Answers as follows:
1. Quality- Manufacturing skills have eroded. Market is very small.
2. Tube electronics were lifeblood of many military and industrial products. Huge numbers of replacements were stockpiled. Soviet- bloc continued to use tubes long after Western countries abandoned them for several reasons. One is that tubes are not susceptible to Electro-magnetic pulse from nuclear blast, like solid state devices. Soviets preferred to use tubes instead of trying to shield their electronics.
3. When NOS are gone, they are gone. However their apparent longevity is exaggerated by large numbers of unscrupulous people selling used tubes as NOS.
I've also wondered about this. Audiophiles are willing to pay enourmous amounts for cartridges, interconnects ...etc.

Could another reason be that the older tubes used materials or processes that could be considered hazardous thus they couldn't be manufactured anyhow?
My mother was the one of the highest paid workers on the Sylvania tube assembly line for many years. She could do all the jobs from start to finish and would train the new workers. She worked there from 1943 to 1957. She is 83 now.

You guys will cry because she says they use to throw out tubes that were absolutely perfect in every way, except the Sylvania printed label on the glass or the base was crooked, smeared, incomplete, etc. Too late to fish through their trash...LOL !!