I get bored with the lack of materially different things to do in vanilla. Automation really has to be a major component in my game, and the resources required to do that in vanilla are generally absurd or abuse bugs or "gaps" in the game that pretty obviously were never, and would never have been, intended by Mojang.
Hence my love of mods. They add enough content to keep me interested... but even barring that I still rush to endgame, become unkillable, and the game becomes "Grind in the mine for materials", "build the same thing I've built before", and "stare at a place thinking 'I need to put something there', yet never following through".
Which is what this challenge excels at breaking. It gives structure without being (usually) prescriptive, it limits with clear unlocks, and it focuses on a non-progressive component to do so.