[Bartweiss]

Perhaps you live in Turkey and Google Public DNS is blocked?

I agree that on a privacy level, hiding DNS requests from Google when your Google Chromecast is calling Youtube seems like closing the stable door after the horse is gone. But there are reasons other than privacy that relying on Google's DNS might go wrong; it can be blocked (or trigger suspicion) by a government, ISPs have occasionally broken their routing to 8.8.8.8 specifically, and Google DNS itself has even had (very rare) outages.

None of those issues are enormously common, except perhaps Turkey's censorship, but they're all totally avoidable. Using 8.8.8.8 as a default and failing over to the user's DNS if necessary seems to be strictly better than this approach from a consumer viewpoint.

[shawnz]

These are good points, agreed. Thank you

[sowbug]

Chromecast isn't sold in Turkey. That fact doesn't invalidate your general point. But pragmatism easily wins when balancing all the real-world craziness of captive portals, ISP DNS hacks, and creative name-resolution optimizations against "but it could be grey-marketed in Turkey." This is especially true for a narrow-purpose consumer-entertainment appliance that already depends on other services provided by its manufacturer.

https://support.google.com/store/answer/2462844