For gen 4 and 5 games, PKSM needs to hijack Poketransporter's permissions in order to read their save files. If the Poketransporter app hijacking only worked if you currently have a Pokebank subscription then this app would only work while your console is connected to the internet. The reason for this is that your console would have to connect to the internet to verify that your subscription is valid before granting permissions. Since gen 4 and 5 games work offline in PKSM, that means that actually purchasing Bank isn't needed.