Reincarnation is a phenomenon. A fact in manifestation, like everything else.
In physical life, we assume the identity of a body and a personality and experience the physical plane. On the inner, subtle planes, we assume the identity of a soul, or whatever name you want to call the subtle bodies.
For some time those subtle bodies like to repeatedly inhabit physical bodies.
It is based on desire. The desire to experience the physical plane and the multitude of experiences it provides. The desire to wear different garments and show off and interact.
If there is no desire for incarnation there is no incarnation.
Cause-and-effect is largely responsible for the arising of that desire and the series of incarnations that succeed. The desire to pay and to be paid and even out accounts of transgressions that occur on the physical plane.
I hear that later on, for older souls, incarnating can be an exclusively altruistic business. Servers do that. They get a kick out of help those who suffer. There is no better or worse. There is no one to judge. For others they just want to get out of here as soon as possible.
All this has nothing to do with spiritual realization.
Desire is the element water. The Wheel of Fortune sits in water. The Marseilles Tarot aptly depicts what I said about reincarnation, and more, in one symbol.