It's probably one of those things Italian cuisine stole from the French, because every ragu or bolognese starts with a "soffritto" of carrots, onion and celery, and often some cured pork as well, like pancetta.
I can buy that. I've used celery, onion, and carrots in a bolognese before. Just didn't really think about it since I used it for like every soup I make and it was just familiar lol.