Why does GOG lag behind anyhow?
Mostly because unlike Windows and MacOS updates (which rely on Galaxy™) Linux ones should be uploaded manually.
And I believe recent layoffs of Linux-related staff contributed a lot to this.
I had read, the layoffs were of their own Web-Store staff and that they even hired more people in other areas.
One explanation could be, that the Linux version is the only one not derived from a Galaxy version imho .