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

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

A lotta folks think all tubes sound the same, or essentially the same. Wouldn't vendors selling new tubes be inclined to market their product as being superior to NOS tubes, just like the NOS tube vendors, you know, for the profit to be made? Gosh.....another audiophile debate in progress. As for myself, I'll stick with WWII tubes from Sylvania and Tung Sol. Y'all can divvy up the new stuff. :-)

What price glory? My NOS tubes (two 6SN7GT and a Tung Sol 5u4g rectifier) along with tube dampers set me back as much as the headphone amp. Is that wrong?