That happen with other games too. Somewhat there is only one slot for updates in a way GOG offer content management is my guess. Maybe its cost reduction that way. More slots, more expense. But indeed, this his truly nonsense. Having massive bandwidth loss that way. But as some told already, if GOG like to carry the weight they can have it.
Well reinstall sucks and waiting for download sucks too. Developer know the problems very well. They could develop Patches adaptive so one file gets just bigger and keep all the patches in it. But well, my guess, the bigger the patch file, the more expensive is it. So developer stay simple and abide by the stupidity GOG price management lay upon them. If only there departments in cost control would talk to each other. But my guess is, even half a zlotty more is worth the trouble with the community. I dont think that there is more gain in it then that.