why don't tubed amps have headphone jacks?

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

My Tenor 8.5's have two jacks

Heh, look at me all learnin' and stuff.