GOG stands (or stood idk) against DRM measures, to which i would count gaming in a cloud with uncertainty if you would get your savefiles if you want to continue offline, therefor your possibility to play a game is bound to being online, etc.

That said, you can still get all your games as offline installer. With cloud gaming they are trying their best to stay relevant / competitive in the market, so good for them. I still buy my games on GOG if it’s available, but won’t play in the cloud.