Every time you install something from GOG, the executable is set to require admin rights in order to run. I get that in some cases is necessary, since some games will try so put the save files and configs in the same folder where the game is installed, but many games don't do that, and it's annoying to see the UAC window every time you lunch the game unless you manually uncheck the checkbox that requires admin rights.

Wouldn't be better if there was an option in the Installer to not do this? Or even better, why not just set the executable this way only for those games that truly need it?

That's not how it works. Security checks are prompted by Windows whenever it's detected that the program wants to make changes outside its designated Program files folder and corresponding app folder. Windows XP and earlier never gave warnings about it. If you want to avoid them, either disable UAC (not recommended) or install the games to C:\ and not C:\Program Files

Actually this is wrong. GOG sets the exe to require Admin access for most (but not all) games, even if they are installed in "C:\GOG Games". You can manually find the exe and unset "Run this program as administrator" if you want but this is tedious

I know because this is true because it often annoys me.

Disable UAC, run as the hidden Admin account, remove all security layers. This is the best way to manage a system, because GOG know best.

It's generally not a good idea to completely disable UAC on the client side. But I do agree that GOG's games shouldn't require admin rights every time. Only a few older games should require it.