FYI there are/were aircraft around that “produce” DC .....and they then often have to have inverters installed to get the AC power needed for any components needing such a supply.
Leaving aside the school answer about AC and transmission losses (which may or may not be significant with airframes) I’m guessing AC has the advantage of being able to be transformed/rectified to other voltages and/or rectified to DC as and where required around the airframe...it might be harder/less convenient to do the process the other way.
Awaits incoming....