Why do NOS Tubes sound better than new tubes?

That’s funny, I asked this same exact question to a local high end audio shop nearby. "Deets Sound Room" in Carmichael, CA if you know the shop. I was giving pretty much the same answer as everybody here. But I bet if you ask that same question today to tube makers, will they give you the same answer or will they give you some marketing spill??
I was personally thinking myself tubes made today would be better than the NOS due to manufacture process today could produce a better quality tube. You would think its being built better today, but I guess that’s not what I'm seeing to all the answers. No pride in tube making today I guess.

Don't write EVERYONE that manufactures tubes off, just yet! These guys are making some VERY nice tubes currently: (http://www.euroaudioteam.com/en/products-000002.html) Much can be done with excellence(even these days), IF you take pride in your craftsmanship. YES- It costs!

As far as the sound is concerned, I'll attribute the decline to significantly decrease competition and demand (like many of you have already indicated).

For the build quality, durability, and lifespan, I think it's the shift to a "disposable" society. Cars, lower-end receivers, washers and dryers, telephones, televisions, mass-produced furniture, and so much more just don't last as long as they used to. That's not to say that they're not functionally better in many ways; they just don't last as long. I've had a cheap gas stove from the 50's, and a cheap gas stove from the mid 90's, and while the newer stove is safer (avoiding pilot light issues), the older stove might still be functional in another 60 years while the new one might crap out tomorrow. It should be no surprise that vacuum tubes (no longer built in the UK, Germany, or North America) also have shorter lifespans.

Rodman makes a good point. There are a couple companies out there that make excellent new productions; however, EAT for instance is limited to the KT88, 300B, ECC88, and the ECC803S, and that's not all that uncommon. Heck, the only current production 5751 is the Sovtek (as far as I've found). There are some very good options out there, but not for everyone (certainly not for the rollers).

Personally I prefer the NOS tubes. They also seem to last a lot longer. The exception is EAT. The problem I have with EAT KT88's is I bought a quad of used original KT88's that have serial #'s that start with 'D'. 1 is bad after 25 hrs and 2 won't hold a steady bias after 100 hrs. The pair I have that start with 'E' seem rock solid. So as of now I only have 3 good ones. That being said the sound from the EAT's is something else. Just got some Gec KT88's that sound real close to the EAT's and being vintage tubes I hope the last a lot longer.