why don't tubed amps have headphone jacks?


I can understand that vintage amps usually didn't because the state of phones in the 50's was rather primitive and phones weren't useful 'til stereo came in strongly. Why no phones jacks now?
joe_in_seattle
Trucker/Mezmo; one of my favorite pair of headphones was the AKG K1000. It didn't even have the normal 1/4" headphone jack. It connected directly to the speaker terminals. People have driven them with all type of amps!
I have a Gini Audio Space 6i intergrated tube amp.
It has a really nice headphone output and it can play loud.
It uses KT88 output tubes and amp is really built.
Here's a pic of it.
http://www.gini.com/index.php?id=int-amp