NASA has spent so much time on building the station with solar panels but did not consider an add on which was a power unit, so match that logic with a deadline and you got something even better than what NASA started out with for the space station's power unit becoming a seperate unit entirely which also could be jetisoned away if necessary. So why not start planning the stages to bring that to the station as soon as possible and make the main power unit that while having a backup power unit the one which has failed and can be repaired over time. Maybe a guess, but something some female forgot to do was to sweep out the joint properly knowing this could slow down a successful flux (of power).