I think the GP post might have been downvoted because "what the math is useful for" frames it in the wrong way, making it sound like every lesson needs to be immediately applicable to your everyday life. An honest answer might be "this lesson in fractions is one step on a difficult 15-year journey that culminates in a junior developer position at OpenAI," but most 10-year-olds aren't ready for that conversation, so "just trust me, bro" might be the best we can do at that point.