There are a lot of issues with Chromecast in general, not just for Oculus. But, the official statement is that a Chromecast gen 3 or Ultra is required. I think is because the older Chromecast devices do not support 1080p 60fps and might even lack some decoding functionality needed.
The other official statement is that casting is on a per application basis. This is because a application creator need to handle copyright rules for their own material, Oculus can't be responsible for that.
BTW... If you reeeeealy want to stream video out of the Quest it is possible, but a bit of a hassle. But! The youtubers "Cas and Chary VR" made an excellent how-to video on it: https://youtu.be/Ora7OrQHwEs