Balance and flavor I think. In general a High Elf is considered to be "smarter" and more attuned to Arcane study, so they have a cantrip that is tied to Intelligence, the casting stat related to study. Wizards, Fighters, and Eldritch Knights all study for their magic and thus use Intelligence, and so it is the same for a High Elf or High Half Elf.
By comparison a Tiefling tends to use Charisma for its innate spellcasting as it is something that was granted to them from their fiendish blood, similar to how a Warlock or Sorcerer has been granted spellcasting due to some entity or thing and now just can cast spells naturally/unnaturally. A lot of why certain stats pertain to certain abilities is the flavor of it, how it fits the race or class.