Simply put, because Comcast wants you to use their own On Demand platform to stream HBO GO on your big screen. It's worth noting that HBO doesn't have the exact same agreement with all providers. Comcast may have skimped on their payments to HBO and cut corners by not authorizing the service on the more popular platforms. Word of advice: Get a Chromecast. If it's available on your phone, it's available on the Chromecast. HBO GO supports Chromecast, so it should be a no brainer. Just get the $35 dongle.
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