Why aren't new vacuum tubes as good as old ones?

.... b/c back in the 1940s to the 1980s, the quality of the tube was literally a Life/Death situation during the COLD WAR and all the millions of pieces of military gear from complex communication systems to airplanes (as noted, for MIGs to withstand the Atomic Cloud after an A-bomb goes off--> since the transistor designs could NOT withstand the Atomic Cloud and would fail ... mid flight in the MIG).

Note all the later model cars running around with burnt out lamps (not LED's, a different story altogether regarding solder joints and high temp LED's), and yet I bet there are 1958 Chevy's with original bulbs all around the car. I never replace the old copper bulbs in vintage units if they are still good, as they will outlast any new bulb.

I have heard some tube types say the "quality" of the parts/spotwelds and the purity of the vacuum itself is not a good as it was before Solid State. Could be the same with today's lame ass bulbs.

and alot of those people that made tubes back in the day have passed and the EPA aspect is more stringent in todays world.

Because old ones where made for war...new ones are made for audiophiles...although there are few new tubes that exceeds expectations...

Nobody knows why. If somebody did they would certainly be able to make exact duplicates.