Prakṛti is imagined as a singular entity (all of nature), but it is manifested in each of us as part of that totality.
By contrast, although Puruṣa represents an encompassing “Spirit,” it appears differently in each person, because each person has a different temperament or “spirit.”
So we can speak in terms of multiple “puruṣas” (each individual person as a manifestation of an encompassing cosmic Puruṣa) (compare to ātman as a manifestation of brahman).