G2A never will use them, it's a stolen key proxy.
CDKeys is a better option, as it only sells it's own keys direct.
I only get GOG games here on GOG, the only exceptions are crowdfunded games, where I've always chosen GOG as the site I want the key for.
Dreamfall Chapters gave me the GOG key through Humble, others just emailed the code to me.
I don't come to GOG for the best price, I come for the DRM free, offline installers.
The best service costs more to provide, a price I'm willing to pay, to keep my GOG games, without using a useless store client,
Though I want to have the choice, so those who like store clients, can use what I will not.