If we represent the total of all the elements in Earth's crust by a roll of toilet paper stretching from here to London, rhodium would make up just this much.
When we look at rhodium and it's neighbors on the periodic table we find a lot of stuff that's ridiculously rare, at least in Earth's crust where we can get to it easily.
That little thing on your exhaust that you've probably never looked at, is a literal treasure chest full of valuable metals, platinum, palladium and this one, rhodium, the most expensive metal on planet earth.