Integrated Tube Amps with Subwoofer out?

I’ve only seen subwoofer outputs on a couple of integrated tube amps (Rogers & Rogue) why is this so uncommon and are there any others I should be looking at? 
The Rogue Cronus Magnum III has a phono stage too, which make me like it even more. 
You can use this for $40- Russound ADP−1.2 Speaker Level. I used this to run dual subs out of Leben amp.
Itis not necessary to have a preamp out for a Subwoofer,crutchfield sells a adapter 
you just put a awg 16/wire in the + - for each side of adapter ,and either a 
banana or spade into speaker terminal it is actual more accurate 
and crutchfield , or call SVS subwoofers they can tell you exactly what it is called for under $30 I used one with my Krell integrated worked great. 
Primaluna integrated amps have one. All tube. 
Decware has a line out intended for subs as an option. They add tube rectification which is awesome too. 
Use any integrated you want. Simple elegant solution. Give Jensen a call and they will set you up with any type connection that fits your situation. Under $200 I believe, very friendly service.