Light-Seal® is a patented technology* that swages the end of the connector to secure and align the fiber concentric to the outside of the connector ferrule, thus assuring minimal lateral fiber offset when the connector is mated to another connector or to an active device.
This technology also serves to minimize the probability of contaminates in the connector between the fiber and the Connector hole.
(This is very likely when you polish the connector with lapping paper and liquids)
*US Patent 6,517,255

Light-Seal connectors are made to swage the end portion of the metal ferrule connector which lightly holds the fiber and aligns the fiber concentric to the outside diameter plus holds the fiber independently from the cable jacket so no epoxy or adhesives need to be used
A big challenge in maintaining the low cost of POF connectors is accurate alignment of the fiber ends in a mated connector pair. Misalignments on the order of mils can produce insertion loss that is measurable and of concern to end-users.

Final alignment is driven by component accuracy in the individual connectors. Connectors are held to the tightest dimensional tolerances (Hole ID and concentricity) allowed by state of the art manufacturing equipment and processes.