In LibreELEC once Kodi runs it opens/owns the alsa sink preventing anything else from using it, so audio MUST go through Kodi to reach the audio hardware; ergo Kodi is the only place to implement something. General purpose desktop distros will be different because they typically implement some other layer, e.g. PulseAudio or PipeWire, and Kodi runs audio through them, so Sendspin integrates there to reach the hardware. LE can also use them, but PulseAudio has rather limited support for pass-through audio (a popular feature with users) and PipeWire either has similar limitations and/or isn't so well supported once you move away from the x86_64 hardware (me is forgetting which) so there's always a compromise and hence we don't use them by default.