Why does dish network down convert some channels to SD?

Dish's National PBS feeds have been SD for forever.
What aspect ratio do they present them in?

PBS itself transmits the national feeds of its SD channels (Create, World, and First Nations Experience) in widescreen. With adequate bandwidth to make them look good, of course.
I watch the NASA channel a lot, there's tons of great stuff on there and you're not beset with garbage ads all the time. It does look lousy though. I have their app on my phone and can watch it there in HD, but it's not the same as a TV. International channels look terrible too.

Hopper Grounding ... Cheater Plug

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