I am aware, that Apple / MacOS is not a big scene in Gaming, though it sees increased support in recent history.
However, i am not about older games that run in a mock-environment, but about newer games. Things seem to be quite inconsistent. I.e. Factorio has decided to support Apple M-chips and released a installer for MacOS, which you can get on GoG as well. Frostpunk 2 is available on MacOS, available at the Apple Store, Steam etc. but on GoG, you somehow can only get a Windows-Installer.

How come and why is it?
Plus, on the side note - the Galaxy App is still running via Rosetta

There's a few reasons. Least of which is Apple's "Screw you, pay me" policy, to which I understand is a monthly or yearly fee just for the privilege of signing applications.

Which is dumb, because modern MacOS is nothing more than a bastard stepchild of Unix.

Developers have the choice.

Steve Jobs strikes even in the afterlife. Macs are great for Photoshop and prepress work comercially, but Jobs and Woz never seriously contemplated the gaming arena, considering it "Walt Disneyish." The original Macs were b&w miniscreens back 40 years ago. Even IBM PCs of that era had bigger monitors.

That would be why.

You'd have to ask the developers/publishers why the Mac version isn't on GOG. In a very few cases, it's because Apple paid for the port and it's only on their store (e.g. Resident Evil Village). Most of the time they probably just don't consider it worthwhile.

As for Galaxy, it's barely updated on Windows and doesn't exist on Linux at all, so.... I'd guess it has an ancient toolchain where they can't just flip the "make universal binary" switch. That's ignorant and false, as always from you. Don't you get tired of being wrong all the time? If the Mac version's on Steam, they already paid the signing fee (which isn't monthly, lol).