One of the major reasons for closing the source were fake or cloned apps being distributed on the app store. Even in case of "benign" clones, their developers would keep all support links and the official logos and branding. We cannot provide support for modified versions, and both malicious and poorly implemented "benign" clones were having a negative effect on our image and ability to provide quality support for users.
the only thing an attacker needs for creating a malicious copy of a wallet is the name of the wallet and absolutely nothing else. the looks of the wallet can also be different, even the logo. a user that downloads such malicious wallets doesn't pay attention to those differences either, even if they do it would look like the new version's new looks. and since the attacker's intentions are to steal user's money the malicious wallet doesn't even have to provide majority of of functionality that the wallets normally do.