This is only half of the reason.
The big Twitch stars are why people come.
The way the system/GM/players highlights cool, badass and sexy characters is why people stay.
The viewership wasn't bad to begin with. There was enough artwork and ads for people to join the show. But for me the show never got it's velocity.
If you tell the Blades story so far, it sounds amazing, but the storytelling is hidered by the ruleset, and that's why we never get a 'Are you ready?' moment from Marcus or a SpikeSpace walk moment from Geoff. We never are in the moment. It's planning for the moment and living the effect/repercussion of the moment. The moment never happens on the show.
RPGs are a conversation. With Adam it's bathing in the feeling of a situation, exploring the emotional angles of every choice. Sicarian is about to go for a spacewalk and Adam gives him a little scene with one of the female Pfotenhauer officers, building up the fear, the uncertainty of the situation, allows Geoff to express fear/courage, to be a badass (what Geoff does best) and a 'maybe we meet again, if you live through this' type of romance.
In Blades it's discussing how awesome it would be to do something and how to do it, and then discussing how awesome it was to do it. You barely see the moment it's being actually done or feel what charactes think when it happens. If anything, you see their actions, and while behaviorism makes for a deeper experience, only a sublime group of viewers will find it entertaining.
Wheat or Geoff are ready to express their characters, but BitD is just not the system that encourages that. And John, being a strong advocate for his system, is not helping.