Guest post by "Jasae Bushae" I would theorize the reason is because the minor arcana are connected to elements and it was their combinations which resulted in the worlds creation. Plus, it has been shown that aces who are tecnically the weakest were able to create arcana's with no trouble so power shouldn't make a difference. Though I am kinda curious if they ever tried mixing with other Arcana's to see what happens.
Plus, im sure the fact that they were created from the dreams of the 'afterthought' life that came of the worlds being created in the first place has something to do with it...