The adventurers of the first Harbor of Hearts found an enclave of poppets deep in the heart of ruined Absalom. They were led by a cruel poppet who named himself MYSELF.
The writings reveal that MYSELF was a very lonely and very selfish person. He sought companionship in the form of more poppets like himself, but not equal companions. There are pages and pages of failed experiments, some of them quite vile, trying to awaken new poppets.
Eventually, he discovered that poppets awaken when they have a spark of life placed into them. Importantly, the spark has to come from somewhere. It isn't created ex nihilo during the awakening. Some poppets inherit fragments of the dead or the undead. Some poppets inherit a tiny sliver of the spirit of someone who wishes fervently for their life. Many poppets receive their spark from the nature spirits that roam to and fro across all of Golarion.
Not the full-fledged spirits of the Fey. No, rather, the low-level common spirits that inhabit rocks, trees, caves, and villages. When the former spirit, or spirit fragment, of a Marked is used, those Poppets awake Marked. MYSELF has several pages musing about how a spirit fragment comes to be, but is ultimately unable to answer the question. Whatever the case, death is a tumultuous and messy process and it seems perhaps bits of spirit may go astray from time to time.
And so he concludes that the best opportunity for arranging for the awakening of a poppet is to place it in a portal, like a window or doorway. This creates the ideal opportunities for allowing a poppet to "catch" a spark as it passes by. Exactly what causes a poppet to pick up a spark and what causes it to pass it by is something MYSELF never discovered.
MYSELF filled Absalom with poppets of his own creation and hung them in doorways and windows. Many of those poppets are still there today.
Since the Second march, however, poppets have begun awakening normally again. It is one of the true wonders of their accomplishments. Any poppet younger than 75 years old may have any backstory they wish. They may still, however, be Marked, if they happen to awaken in the way MYSELF discovered.