It’s not GOG that does that. A lot of developers that publish there having lost the source code or the tools and knowledge to build it upload cracked or patched releases themselves. And it’s not a GOG thing either, as for example Sam & Max: Hit the Road is just the cracked DOS game bundled inside a ScummVM runner on both Steam and GOG releases.
You literally cannot see the contents of the game without first decrypting it. Your internet connection is encrypted, your device is decrypting it with its known keys. You would not see the content of your Lemmy instance if your device didn’t decrypt what it received.