keeveek: Something like GameRager said, also wishes like "Activate already owned (e. g. on Steam) games on GOG " should be gone. They're just littering the wishlist.
Rejected also for wishes GOG has no desire to complete - why giving useless hope?
Why? Just because people don't agree that the idea is wholly feasible doesn't mean that the idea doesn't belong on the wishlist. There is no reason why such a feature cannot be implemented in practical terms, at least with certain games.
CDP started the ball rolling in this field with certain titles, Almost Human did a similar thing by allowing purchases from their website to be transferred to GOG. Granted, it's not really feasible with very old games like Doom, but with games that had CD keys, I see no reason why this shouldn't be possible. I assume companies like EA still have their database of CD keys to hand that they issued for various games post-2000.
After all, the vast majority of people who had already bought a game on disc are not going to go out of their way to buy it on GOG. GOG has a choice in this regard - sacrifice a little more bandwidth for these customers and keep them coming to the site, or keep up with the hope that they will eventually buy the game on GOG.
I'm posing a theoretical situation here. I know the circumstances, especially with older triple-A titles, make it very unlikely that such a feature could be provided, but with certain compromises it is feasible in terms of licensing and tech to provide transfer services with selected games.