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

Current tube production is aimed at a small niche market.  Before transistors, tubes ran our electronic world.  They were critical and manufacturer's had to make quality product for the military, government and..  We are the hobby market and really don't amount to huge profits.

Yes but current tube production is not critical to the communications business, like in the past. Tube makers could do better but where is the motivation.  Product longevity does not keep the line moving.