Current tube Manufacturer's as good as NOS Best

I have been reading with interest many of the posts on tubes and have come to the conclusion that NOS tubes from 40 -60 years ago sound better than tubes from current manufacturers. Why is that? If that is the case then why hasn't some manufacturer come out with a tube that competes with or betters the old stuff. It would seem that with the current popularity of tube equipment someone could come up with a better product. Curious to hear some answers.

Eagleman