Redbox and Crackle, I believe were both owned by Chicken Soup for the Soul Entertainment, who went bankrupt and took a lot of brands and streaming services with it. I can feel your pain as I was a fan of the rental Kiosks of Redbox.
That may be the case for Cinema box as well, especially now as there are a lot of mergers and contraction of streaming services and bankruptcies as a number of these services are finding it hard to be profitable due to the overwhelming competition and cost to maintain and create content.
In addition, as previously mentioned, that doesn't include apps that are playing content that they are not legally entitled to do or have violated copyright laws that get shut down from time to time. I can't say that is true with Cinemabox, although I have read some rumors that may have happened.
As Makalguy stated, Roku has little control over those individual brands/apps it doesn't own, which is the case for the majority of apps on Roku devices.
You could always attempt to contact customer support for Cinemabox directly (instead of Roku) and see if they respond and could provide more specific information for their app being down or unavailable. It may be something as simple as a technical or server issue on their end.
