There's a lot of great stuff available through Good Lock, but there are also a ton of features that not everyone would use. I'm happy that Samsung doesn't bloat the OS with more features, but still makes them available to anyone who wants them. With most other Android skins, you get what you get and nothing more.
Keeping Good Lock separate allows Samsung to provide simplicity and ease of use for the vast majority of users.
Requiring Good Lock to be downloaded allows power users to have a robust suite of customization options at their disposal without overwhelming users who don't need or care about those things.
