I think you're dismissing the fact that bionicle is a toyline for kids. ANY question you have for BIONICLE has probably been answered already, and the answer is most likely something to facilitate further story potential. An example being that we'll get rough numbers never an exact amount of how many Toa there are at any certain time- it limits the potential for future stories.
Furthermore I think you can seperate alternate realities and pocket dimensions into separate categories. Some are made intentionally by intelligent beings and some adhere to multiverse theory.
Again, it's a toyline first and the story exists to help sell those toys. I imagine every creative decision will forever and always adhere to that.