roku curate channles are on its platform

Roku is a platform, and almost all content available is from 3rd parties. Roku does offer their own content via The Roku Channel, that they license from content owners. 

Roku has terms of service that channel providers must comply with to offer their content on Roku devices. Those rules do have some restrictions on content. Beyond that, Roku has no control over content the providers offer. As long as they do not violate those terms of service, Roku does not "curate" the content of 3rd party providers.