By putting it in Creator Packs, it lures people to go to the PS Store, also showing them other things, that isn't free, which could make them buy it, without really having had any thoughts about it before.
That's why they most likely put it in Creator Packs.. Also, if they have alot of stuff to add (Checkpoint Switches, Material Creator, Wind, Automatic Thermo reductioner (Material changes, where it's not necessary to have that material in particular) fx), it would be easier for new players to just start with something easy, without wandering around lost in the world of DLC.
@ARD: As I'm new to LBP Forums, I wouldn't know if MM checked forums often, at all, or only looked at stickied topics etc. ;)

