Content owner/providers make apps for Roku. As for exactly “who decides”, that’s a little complicated: First the content owner has to decide that Roku has enough market share in their region to be interesting. Then they have to decide whether they like Roku’s terms for fee and/or advertising sharing, or come to some other arrangement with Roku. So, it’s mostly the content owners but they could always blame Roku’s terms, although the other providers you mentioned can obviously live with them.
Banned but back. Because why not?
