For me, I guess it’s just that foo/bar is standard and fewer characters so it’s the obvious and ergonomic choice. But we can’t use that because of infix math, which is also a choice. So why are the choices made that way? “We made it easier to write mathematical notation at the expense of making it worse to talk about every namespace” isn’t the best trade off all the time.

No it's just a personal opinion. I like the UX of using dots for everything.