They "market" it to the wrong audience
Disney has been doing this ever since they first tried bringing back Tron. Keep making the same mistake. They target new audiences exclusively, and pretty much ignore the existing fan base whenever they make decisions. Because we're the "sure thing".
I get that they're trying to appeal to a new young audience, and obviously an animated series resonates most strongly with kids. But by keeping the show pretty much exclusive to Disney X D , they're shutting out many existing fans while focusing almost exclusively on acquiring the new ones.
What they should be doing, is targeting existing fans and letting them evangelize the product in question. Word of mouth is far more powerful than any marketing campaign. If Disney put Uprising on a channel that was more accessible to a larger audience, existing fans would see it and gush about it to all their friends, getting them hooked on it.
Notice how when Disney hired 42 Entertainment to promote Tron Legacy, they decided to target existing fans by creating a Flynn's Arcade and building upon everyone's fond memories and nostalgia of the original film. It was a huge success, everyone was talking about it. But whenever Disney does the marketing themselves, they can't understand this basic premise.
I really hope a way can be found to improve the ratings and keep Uprising going. That Disney will wake up and see the light. Tron Uprising is just sooooo good.