Why do NOS Tubes sound better than new tubes?

Also Western Electric and RCA in the film industry sought after better sound. Most likely another big profit area.

That would explain why old movie soundtracks sound so much better than any other old audio.

I was told that new tubes aren't allowed to be made with the same rare metals that NOS tubes use. They are heavily regulated and folks high up on the food chain don't want them readily available to anyone who might want to use them for something else.
All that leaves the newer ones with are better engineering, closer tolerances, innovation and cleverness.

I have heard the same thing about the metals used and that they are not available anymore.

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.