I can't get DTS sound to work on my 4K Apple TV

There is currently no support for DTS audio on Apple TV hardware.

Apple TV 4K (2nd generation) - Technical Specifications

Audio Formats

HE-AAC (V1), AAC (up to 320 Kbps), protected AAC (from iTunes Store), MP3 (up to 320 Kbps), MP3 VBR, Apple Lossless, FLAC, AIFF, and WAV; AC-3 (Dolby Digital 5.1), E-AC-3 (Dolby Digital Plus 7.1 surround sound), and Dolby Atmos

That shouldn’t be an issue, as none of the streaming services use DTS.

Infuse has its own DTS decoder, giving support for this format, while Apple TV outputs it as PCM Multichannel of the same quality.

Infuse and audio options (tvOS) - Firecore

Requests only gain traction if there are enough requests, if there are not enough "asks" then you are likely correct. Are you aware of any other brands of streaming devices that have Apple's functionality that do support DTS?

You can also let Apple know by submitting your thoughts at www.apple.com/feedback.