Question about Locket/Banner

Maybe I'm just over thinking it but--- Why does Locket offer the better resistance against magic resist and Banner offers the opposite and better option for armor?

Locket: 60 armor, 30 magic resist Banner: 30 armor, 60 magic resist.

Wouldn't it make more sense to have those options swapped? Anyone buying Locket tends to encounter more physical damage in the support role while buying Banner gives a minion immunity to magic damage and yet provide more armor.

I don't get it lol.