As soon as I find out how to do it, I’ll do it very willingly! :D
Reading in forums, it's my understanding that only paid games can be claimed: including a paid game which is on sale, or even free for a limited amount of time.
I may have misunderstood, of course, but it seems a reasonable explanation; since paid games are claimable by default.
As a dev, I still have the option to make my paid game not claimable if I want.
Apparently, this is why I can't make Their Eyes claimable.
Even if you pay fifty bucks at the download, it's technically a donation - while the game remains free. :/