They're unlike the purely free form journals and also unlike the guided but unstructured journals that offer different, random questions and prompts on each page,
We intentionally use the same research based questions and prompts each day. Studies show that if you're addressing new prompts each day then it's more difficult to build a regular journaling practice. Even if you're able to develop a journaling habit using only Unstructured or Free Form Journaling, these methods are less effective in empowering you to reach your goals.
That's because in these styles of journaling you're not using a structured toolset to practice an effective habit, you're simply engaging in a hobby. When you focus on the Legendary Journals' simple, powerful, consistent format you drive towards goals while also creating a record to look back on how far you've come.