Why do some Mopars rust all to hell, and others go for decades with no major issues?

The first time I noticed the phenomena listed in the thread title was in the mid 1980's.

I noticed that 66/67 B body cars, as well as 70-72 mone carlo and 71/72 torino didn't rust out nearly as bad as 68-70 Mopar B bodies and both earlier and later fomoco and gm intermediates.

I started my Mopar journey as a 66/67 B body guy, so I became intimately familiar with them.
Another thing I noticed was that 2 door cars, if they did rust, rusted bad above the rear wheels.
4 door cars did not.
I learned this is because 2 doors have a direct path from the wiper seal below the rear side window, to the pinch weld of the outer wheel house and quarter panel.
4 doors have the back door, and another layer of sheet metal in the way.