Hello, I suck at creating titles and this is my first theory. It just came to me, and It probably sounds foolish but here goes. When the Rikudō Sennin divided the 10 tailed beast into 9 distinct biju's, I think he also sealed a small portion of his own chakra into each tailed beast. I think it could have served a dual purpose.
First I think that with the infusion of his chakra it allowed the tailed beast to live. How else can you split a person and create basically a new entity out of it?
Second I think that this is also a fail safe, if for any reason someone ever wanted to reunite the tailed beasts, I think it will also unleash a seal. Maybe it could lead to the Sennin's return like Minato or Kushina did. At least only to the extent that the sennin would return to try and prevent the rebirth of the 10 tails.
I don't know but this has been on my mind since the whole 10 tails story being introduced, maybe it doesn't make sense but these are my thoughts, thank you.