When a developer plans to build a product, the majority of them will fall on one of these ideas initially - especially if they do a stunt at trying to build several products before they quit:

To do app
Journaling app
Travel app
Note taking app
Calendar app
These are the top 5 ideas they get, because that’s the environment of tools they’re working with. Then they convince themselves it’s a good idea and waste a few months, or years, building them. And eventually get zero users and go back to working for other people’s ideas. So it’s apps around list management.