I considered this, but people and resources don't 'grow on trees'. Ronan decimated their army and reached Xandar's soil, and preventing that from happening was the Nova Corps' single task. I don't think that they recovered much in those 4 years.
Wouldn't it have been crazy if this was a 3-part finale...? I mean, you could also write-in the acquisition of the Aether on Knowhere, though I'm sure nothing as exciting as Xander, there appeared to be no life left there after Thanos was done with The Collector.