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

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. 

This thread is very timely.  I own an ARC Ref 150SE amp.  My amp uses 8 KT-150 tubes.  I either read or heard that KT-150 QC has dropped over the years.  I understand that ARC and some of the major tube retailers have a high KT-150 reject rate.

In any case, here's the bottom line.  I recently spoke with the ARC customer service rep.  He advised me that ARC is selling KT-150 tubes for $265 per tube.  ARC charges over $2650 for a complete retube of my amp (2 quads of KT-150 and 4 6H30s).  Yikes!! 

As an aside, several years I bought 2 quads of KT-150s from a well known and respected tube vendor.  The problem is that even though the tubes were matched, the bias settings between the set tube and slave tube were off by a lot.  By contrast, ARC tube match very close.

Any suggestions?