I think the problem has more to do with GOG rejection of games. (could be wrong)
I think that is part of the problem albeit in reality a small one, the other being things that look to be corrected with Galaxy(either in it's current state or in the near future) such as making it easier to do a DRM free release on top of a Steamworks ladden one since Galaxy API offers the same features just minus a optional DRM solution(Steamworks.api allows you to use CEG DRM if you wish) and depending on how close it is to Steam's API on a code level it you could theoretically swap one API for another without much hassle where in the past devs would have to strip the parts of their games that used Steamworks such as Spelunky's daily challenges for it's GOG release as well as making pushing out patches easier or at least it should. I know one big complaint about Desura was how backwards and troublesome it was to get patches distributed on their service
Another issue is customer base, you see back in the day Steam was heavily curated not unlike GOG and alot of times games would get rejected for no determinable reason. Space, Pirates and Zombies for example was rejected by Valve for two years before it was accepted, no explanation as to why it was rejected and no explanation as to why it was finally excepted after all that time. But the guys behind SPAZ didn't give up even though the game was sold elsewhere, they kept pushing to get on Steam. Why? because Steam had the largest customer base out of any digital store so they like many indie devs at the time, just kept submitting and submitting because they wanted to have a chance to sell their game to the largest pool of possible customers as possible. Plus since Steam was heavily curated at that time, getting your game there meant you were guaranteed front page exposure for quite a bit of time allowing you a chance to try and entice people to at least click on your store link and give it a look and consider buying it.
Really what I am trying to say is it just falls to what offers a better service for devs to use in terms of customer base, ease of use and exposure since if you have a large customer base and it doesn't matter how many times you reject devs, devs will still want to put their stuff on your store because they want access to your customers, especially if can give them some exposure when the game releases on your store.
So yes, we may not always agree with GOG on their curation but I am glad it's there because take a look at Desura before it goes dark and take a look at Steam now they no longer curate their store and tell me that not being picky and risking rejecting the occasional good title here and there is worse then not having any curtation at all.
While I may not agree with them rejecting a Thomas was Alone or another Cat Lady but if that means I won't have to sift through a mountain of shit to find that one game I maybe intrested in, I will live with that because that is one of the big reasons why I didn't really use Desura and why I all but stopped buying games on Steam all together since I just don't want to bother with scrolling past twenty Day one Garry's Incidents, the Wars Z's, Temper tantrums, Survival Z's, ect. to find a Cat Lady, a TechnoBabylon, a Serpent in the Staglands, a Shovel Knight or even a Sunless sea and Sanctuary RPG. I will deal with it, especially because GOG has shown us that good rejected games can still come here we got Cat Lady, we got Avernum: Escape from the Pit, we got Xenonauts, ect. despite their initial rejections especially since the alternative is something I rather not deal with.