Yep, that factor is increased oxidation in the batch that spent a longer time in the fermenter. Unless it's a sealed, pressurized fermenter then O2 is getting in there and the longer it stays there the more O2 will get in the beer.I don't know why it works. Maybe because there is an airlock that allows off-gassing?
Purely anecdotal but in 2013 I brewed 2 batches of Caribou Slobber. One was in primary for 2 weeks before bottling. The second was in primary for 3 weeks. The 2-week version seemed to peak at 3 months in the bottle while the 3-week version seemed to peak around 6 weeks in the bottle. Totally possible there was another factor responsible though.