i think they wanted to put the rear upper arm within the rear wing end plates.
no beam wing this year.
moving the rear wheels forward would alter weight distribution, likely negatively as it seems like they tend to load the nose or tea tray with the ballast. also, i believe the rear wing placement is based on the rear wheel centerline, so moving the rear wheel forward would move the rear wing with it. as it is, they lengthen the back of the cars with unnecessarily long gearbox casings. they get a more gradual coke bottle, it tends to benefit aero.