I believe this is covered in the Wave Series, but as I understand there are apparently 2 ways, the first one is because the Wave, which happened around 306k YA, and apparently it’s already coming again. The second way, is through the interaction with individualized souled beings through lots of reincarnations, since they imitate and reproduce the emotions by interacting with them/us, so much so that they could be able to cristalice emotional centers at one point, which is the beginning to individualice a proper soul.
Granted, we still don’t know the whole concept of what a soul is, but as I understand, is the link between one consciousness with our higher self’s through all developed energy centers or chakras, whatever the name of that is. OPs doesn’t have all energy centers developed, so they depend of fully souled beings to generate their temporary centers but can’t connect with higher selfs still, which would be the difference.