Probably for DRM-related issues. The BBC just made a big deal about warning everyone in the UK that they were sending "packet-sniffer" vans around to identify those people watching BBC programming over the Internet, instead of watching it on a TV (note that in the UK, everyone who watches the BBC is supposed to pay an annual tax per TV set (145 pounds for color, IIRC) for the "privilege" of watching BBC shows live), & they were claiming that the packet-sniffing tech they were using could identify data indicating that BBC shows were being watched, even if the Wi-Fi signal being used was encrypted. They apparently feel that whatever the cost is for those vans, it'll be worth it to recoup it from the fines (1000 pounds & a criminal record per instance).
If that's 100% true (as opposed to just a scare tactic to get everyone to pay their fees), it's not really a stretch for the tech to exist to use packet-sniffers to strip out streaming video data from the data stream & recombine it into a file on another system.
As another possibility, it could be used to prevent the use of 3rd-party "stripping" software, like the apps that claim they can let you download YouTube videos straight from the website. I would imagine it's much easier to do so through an unencrypted website than one using encryption.