Because the archetypical ranger is Drizz't, not Aragorn. I'm sure it used to be Aragorn in the earliest version of D&D, but that changed.
Yeah, originally it was Aragorn, with traces of "Robin Hood, Jack the Giant Killer, Diana's huntresses, and Orion", according to Wikipedia. So wilderness lore (tracking, healing, hunting, camouflage, communing with animals), melee combat (sword and spear) and archery, specialisation against monstrous humanoids/giants or just monsters in general.
And then Drizz't became popular and the TWF thing caught on.
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