Was thinking like you... But I've been thinking a little more and ...
The wish list and its components have 2 different use actually.
1st it lets GOG know with games are highly demanded and lead them to try and get the right for said game.
2nd it acts like an argument, when negotiating with the rights owners. "Look how many people want your game, you let us sell it on this platform and you'll get your share ! It will surely succeed since more than 100 000 people have voted for the game"

Well, you get the idea. A hesitant right owner might accept if he takes a look at the demand for his product.

Okay. Lets see, the world population is not even 10% of that, so I officially guesstimate here that all active GOGers need to create 10.5 million accounts and get voting.

I think System Shock 2 was close to that once, but then you vacuumed the database. :)