Most likely it's a licensing issue. The same reason they no longer offer a DD encoder on the Ultra, so they don't have to pay for a license. But most likely Roku will never publicly acknowledge why they do or don't offer certain features. They refuse to answer why they won't support bitstreaming lossless audio. At least Roku will pass the DTS bitstream via HDMI from some types of media. I know it works with MKV, and I've seen it work with the TS container as well.
Dan
Roku Community Streaming Expert
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