I'm old enough to have purchased them, but don't know why the manufacturer made them that way.
My guess is they were trying to protect the bore in the aluminum.

One of the main problems with mags seems to be what I call "coning in" at the lug holes.
Caused by using the thin washer that comes with mag lugnuts.

Damage can be fairly severe in the oval hole 'Uni-Lugs" since the thin washers cone in, the nut loses torque and after a while the bore can be damaged.
What works in these wheels is to use the thick - about 3/16" thick - Centerline washers.
They spread the load from the lugnut and don't do the 'cone-in' bit.
It looks like your stepped washer/flange device does the same thing.