I'm pretty sure Disney is optimizing for the majority of their audience who use Windows, OSX, iOS etc, not developers/hackers who run desktop Linux. I'm curious about Android though.
I know there are people out there who refuse to run any non-free software anywhere, and it is a good thing they exist, but I would guess that the majority of people who have Linux on their laptop are willing to use a Fire Stick or their TV's builtin OS or whatever to stream TV and movies.
Linux doesn't have a large enough number of users for their consumer-focused video streaming service at this time.
They'll probably move down-market after nailing the experience on the first few platforms.
side note - I love the number of comments about piracy as the other option, as if Disney is reading this page - or cares much about a small market (linux consumer-users)