The reason is that when Minsc was created barbarian was a subclass of ranger and Minsc clearly was designed for the barbarian subclass.
But people associate Minsc with being a ranger and Larian didn't spend any effort on Minsc and thus made him a generic ranger and slapped the default ranger stats on him which by now changed to a pur archer or dexterity weapon build as barbarian was made into its own class.
Not exactly: Ranger was itself a subclass of Fighter back in BG1 days (2nd edition D&D) Barbarian and Berserker were
kits from the Complete Fighters Handbook. People could have applied them to Fighter subclasses too, although a separate Handbook appeared later for Rangers.
