It's cute. "Hello" is just greeting the programmer, as if it were one person to another. "Hello, world" is like a new baby introducing itself to a planet. It's both tiny and momentous; the contrast is humorous. That feels friendly.

Especially viewed in its original context, introducing a new programming language (C) to a planet that wasn't quite as crowded with programming languages as it is today.

Since then it's just tradition. Feel free to leave it out. But it's iconic for a reason.