I think it is the structure and workflow of a bullet journal that makes it work for me. The bullet journal is an organizer, diary/journal and a planner, all in one notebook. As some have said, with the bullet journal system, you only need one notebook to rule them all.
I’ve looked at planners but found them to be too rigid. Specifically, if I want to write down lots of stuff on a certain day, I will quickly run out of pages. With the bullet journal’s system, you’ll never run out of pages to write, unless of course you reach the end of the notebook, in which case, just get a new one.
The migration of tasks is the killer feature for me, as it forces me to evaluate how important a certain task is. Typically I will write down a task on my daily log. If it doesn’t get finished today, it will be re-evaluated on the next day when I start a new entry on the daily log. If the task is not important enough, it will not get migrated and I just move on. However, if it is important enough, I will end up migrating it every day until such time that I finish it. I once had a task that I kept putting off, so I ended up migrating it for 5 days straight. On the fifth day, I got tired of writing it down, I went ahead and just finished the task so I can mark it complete haha.
I could do the same thing on my phone, track tasks and use a to-do list, but I find that they don’t give me the same kind of satisfaction compared to tracking tasks on my bullet journal. It is weird, I know.