I dont see any reason why would anyone who make Tiefling Ranger pick Fire restistance in the first place? O_o
Which is the point here exactly. Larian designed it so that there is no reason to make a Tiefling Ranger with a background in Hell, which would be really flavorful and quite a logical choice. Instead Tiefling Rangers will now all come from some Tundra or Swamp region for mechanical reasons.
It's clumsy design that overlaps with a lot of other stuff like their own spells and racial traits. Like Niara pointed out, it feels like whoever designed this isn't really in sync with D&D and how stuff works.
