Except... that isn't how it works. You have one single chance for a freebie, once you try to win you either win or lose, and either way you are no longer eligible to try again. If you keep clicking on it to add it to your cart to try again you'll just get the promo price in your cart and put a heavy burden on the webserver contributing to slowing the site down without getting any benefit from doing it.

When a company like GOG does a promo like this they have many years of experience seeing how people respond and learning the ups and downs of mistakes over time. If there's one thing any company will learn is that there will always be at least one person if not 50 people who try to "beat the system" or "game the system" so to speak. You know, the people who will figure out how something works, write a python script then launch it at the website pounding the site 1000 times per second to get all the free games or similar... except that just kills the website and people complain, the company investigates, fixes the problem by preventing people from doing that by altering the way their promotion works.

In short, GOG isn't stupid and so repeat button mashing just wastes your time and murders the webserver. In addition, their web server will try to detect abuse and block you from accessing the website. I know because it did that to me once the other day and I was actually just using the site normally without abusing it so their abuse detection was a little hair triggered.

Anyway, keep trying for freebies but once per game is all you get no matter what you try. :)