The ADA regulations were written in the pre-Internet days and do not apply to streaming video, only broadcast and cable television. Rules were updated with the 21st Century Communications and Video Accessibility Act to include all government programming and websites and in "places of public accommodation," especially where goods and services are sold.
Some courts have ruled that the Internet is NOT a place of public accommodation, and thus exempt as a virtual space. As a consequence, it isn't necessary for everyone who uploads a video to make it accessible (think YouTube). That’s why much online programming omits closed captioning.
Of course, closed captioning is desirable and is becoming easier and more affordable, at least for larger organizations. Your best bet is to contact the companies whose programming you like and ask for CC. Remember. Roku just provides the platform (except for the Roku Channel) and each channel does the programming.
