No Collector's Edition content on GOG?

[Qthulhu]

Hi folks.

I noticed a good price on Rebirth as part of a GOG sale, but as far as I can see there's only the "Complete" edition, with the expansion packs - not the "Collector's Edition" with the soundtracks.

I did a search for GOG soundtrack here but nothing came up.

Anyone know the reason for it not being on GOG? It is intended to be a Steam exclusive?

Thanks for any help!