>>55139428It's a reference to Lonesome George, the last Pinta Island Tortoise. One of the Pokedex entries mentions how Terapagos was long thought to have gone extinct after getting caught up in the Earth's seismic changes, so it's likely one of the last of its kind, if not the last, which explains why this one has a set gender
From a meta perspective, this could just be the result of Game Freak's standardization of Legendary encounters that play major roles in their stories. Both Raidons and Ogerpon have set natures instead of random because they aren't just random examples of their species, they're established characters in the story
>The Raidons have natures that boost their Attack/Special Attack to reflect their more aggressive natures>Ogerpon has a Lonely nature to reflect the loneliness of her losing her friend all those years ago. It also helps that the Lonely nature boosts Attack, since she then went on to revenge murder the Loyal Three 