Ancient-Red-Dragon: It's the making of a new offline installer every time they patch the game that requires a lot of work on their part.
And that's a main reason why most games (with some exceptions) never come to GOG until they are already first ancient & obsolete & dead (meaning, never to be updated ever again).
Mjauv: I've seen many releases with patches as offline installers. I'm no software engineer but can that really be that much extra work? Maybe I'm missing something here...
It's not. The user you're quoting doesn't know what he's talking about. There is some minor extra work in pushing an update on other platforms (like if say something is released on Steam, GOG and EGS instead of just Steam), but the developers have no involvement or responsibilty for the creation of offline installers.
Offline installers and their patches are created automatically by GOG. When a new version of a game is released by the studio it's delivered through Galaxy immediately. Everything else after that is in the hands of GOG's automated systems.
The new version is then put into a queue for the offline installer to be created. That's why there's always a slight delay when a new patch releases and there's no offline installer for it immediately, because it's waiting in queue to be created along with everything else that released or was updated. New games don't have that delay because they're already in the system waiting for their release timer to go live.
GOG Staff has said as much before in these forums, and I've had a tech support agent personally tell me as much. No one at GOG is manually creating all these installers, and the developers of the games are certainly not either.