Why did the US build Independence-class conversions instead of designing Saipan-class light carriers from the outset?
Short answerIndependence used hulls already in production for speed, whereas Saipan was the better-developed answer available when more time could be spent on the design.
NotesThe Independence conversions used cruiser hulls already under construction to put carriers into service quickly. The Saipan design allowed more thought and construction time around a larger hull. Their different design choices therefore follow from different schedules and the availability of hulls at the moment they were needed.