The 0.250" (6.35mm) pitch sets the board footprint and the per-contact current ceiling — at this pitch the connector can carry several amps per circuit without exceeding the temperature rise limit of the nylon housing.
The through-hole solder termination suits standard wave-solder processes. The 0.155" (3.94mm) post length gives enough standoff for a clean solder fillet on a standard 1.6mm board.
