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

I use some "vintage" tubes...I like chrome dome Sylvanias and Mullards that "flash." I don't know why manufacturers keep putting KT150s, KT120s, and Gold Lion KT88s in the amps they build...don't they know new tubes suck? They even fooled me into enjoying all of those and thinking they sounded great...some for years...

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.

+1 for Sylvania Chrome domes , the Goldilocks of tubes , not too little, not too much .

How many tube guitar amps are out there? Small niche? I'd bet they're 90% of the tube market...gotta scratch that niche.

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.