The Bijuu were sealed into their previous Jinchuurikis.
My theory is two parts on that.
1. Since the Jinchuuriki harvested that particular Bijuu for most of their life, they resonated best with that one than they would if they were to switch Bijuus. That is why Tobi used previous Jinchuuriki with the tailed beasts they hosted in life.
Or this could have merely been for us readers. I mean if Yugito just busted out the five-tail transformation, us readers woulda been like "wtf??"
2. They weren't FULLY sealed into the Jinchuuriki. The chakra stakes were just a temporary way to bind the power of the Bijuu into the Jinchuuriki.
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In order to be a "true" Jinchuuriki, you probably have to be alive.