Compared to web pages, video storage and bandwidth is a meaningful portion of video CPM or video subscription, so 720p (or, say, 360p for iOS 14 PIP mode) yields significantly different cost basis.

The only on mobile thing may have been necessary for the business model.

> video storage and bandwidth is a meaningful portion of video CPM or video subscription

Maybe "compared to web pages". But very skeptical it's a meaningful cost compared to production or subscription prices. Even going with a third party CDN you're probably not paying more than ¢1/GB of transfer. For 720P h.264 that's about about 2GB, or 2¢, per hour of content transferred. How many pennies per month do you need before it's a meaningful portion of the $7 subscription price?

I very much doubt they made that decision based on bandwidth costs though. They've burned a billion dollars already, don't think they are thinking about margins much at the moment.