Why are older tubes so much sought after

Mil Spec components were usually required to be much better than necessary. That was before cost control became important. Nowadays most military equipment uses commercial hardware whenever possible, which greatly reduces cost, improves (yes) reliability and performance. Also, we have learned to make electronics whose performance is derived from the basic circuit design rather than from reliance on tightly spec'd components and trim procedures.

I am surprised that new tubes are less accurately made. A tube would seem made to order for precision automated fabrication.

I wonder what will happen when all of the nos tubes are gone? and no one will have to pay the outrageous prices folks are charging for them. Will highend audio survive?
What will we do? Lord help us!
Somewhere in this scenario sanity has taken a long vacation but again, we're talking about highend audio where some would say sanity has no place.

On a more serious (based on my post)note,I've had superb results using about six different NOS tube mfgrs,in my phonostage.

The differences in timbre and dynamic shadings have been quite audible.Costly,but worth it(almost),so I stocked up on two back up sets.

I believe there will always be good NOS types available,from some of the better dealers/sellers.

However,like anything "worthy" of collecting,from a bye-gone era,it will "cost you".

Stock up while they are "only" expensive.In the future they'll be "insanely pricey" -:)

Best

By the time these NOS tubes have run out, either better technology would have appeared and make tubes a thing of the past for good, or electricity will be so expensive that no one will be able to afford to run dreadfully inefficient technologies like tubes without their own hydro power station!

Chadeffect, I hope you're right! but history has shown that you're probably wrong. As witnessed by the tube resurgence of the last 10-15 yrs. when obviously newer and better solidstate technologies have evolved, tube equipment is still thriving! So,obviously a lot of people still think dreadfully inefficient technology is fine.
One thing I have learned and you should've also, is that logic doesn't apply to highend audio.