Because you released it FREE, but do not worry about it.
Unless you put redistribution restrictions on it, or they credits themselves or someone other than you as the creator, its ok IMO.
As I said before, everybody and their brother is jumping on the App Distribution bandwagon.
They are just posting any FREE apps they find, so their site has more content, and appears like they are big time instead of little fry.
Be glad about this, because it gives your App more exposure, which means more players, which means more referrals, which means more people looking for a new version later on.
As long as you are credited as the creator, then people will know it is your IP and which developer to look for when buying future versions.
You may want to make a list of these guys though, so you can double check them after you release a game for sale. (Just to make sure they are not pirating your paid apps)
If they do pirate your paid apps, or credit someone else for your IP, then take the usual action of cease and desist letters, and contacting their web hosting service.
Web host are usually quick to take action in IP disputes, because they don't want the legal hassles or bad reputation from it.
Another reason I like FlexIndie, he doesn't seem to be posting other people apps.
That seems to be a disadvantage for him right now, but I think his integrity will pay off in the long run.
Coding things my way since 1981 -- Currently using AppGameKit V2 Tier 1