Until the appearance of chakra, the souls of all living beings in the Shinobi World turned into Yin Release. Massive amounts of Yin Release chakra began to infect and reshape this space, forming a special environment exceptionally suited for the existence of souls—much like a cold-storage warehouse where souls were like blocks of frozen meat, all sealed deep within the Pure Land.
This vastly extended their shelf life.
To put it simply, the Pure Land prior to this had been merely a storehouse for various provisions, possessing no preservation capabilities whatsoever; it had simply served as a storage space to keep those souls.
Chapter 95