Paradox (Obsidian) did test quite lot of different stores with PoE. On this forums we have seen some results of that (like people complaining that GOG version didn't have achievements and cloud saves and how patches were late and how there was no beta patches for GOG version etc. Problems with Mac App store version, how patches are very late for DRM free dvd version and how there is no expansion for it, problems in upgrading to higher tier editions in gog versions, how there are virtual no origin version owners in these forums [this of course maybe because of fact that KS backers got their copies in Steam or GOG] etc.). Paradox probably will use data and experience they have gathered with PoE to decide if they release or not Tyranny to GOG and other stores.
I understand that there are other issues and concerns, I was saying that I don't believe marketing to be a major one
But that's just like my opinion, man