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

Was was told once a while back by a 90 year old English tube guru who also worked in tube manufacturing back in the early days, I think he maybe RIP by now.
He said to me that todays tubes will never match a good NOS tube, because back then they used lots of Nickel in the manufacturing process, and today they don't so much if any as it is very poisonous.

Cheers George