Wouldn't that also be a function of which dying star farted the heaviest concentration of platinum towards a location ripe for eventual accretion into an asteroid?
IIRC, elements heavier than iron are created by stars going nova or supernova within those few seconds after they run out of hydrogen and helium to burn.
Our own sun has a ways to go before it does that, and our main concern before that happens will be getting the heck out of Dodge.
Yes, everything heavier than Iron was made in a supernova. (and the iron itself killed the star, any star large enough to fuse iron reaches the limit where it would be a black hole instead) Although such elements, if the nebula that formed the Solar System did come from multiple star deaths instead of just one, I'd presume it was pretty well mixed during the accretion phase, probably by the time there was a recognizable protoplanetary disk.
Earth does have a LOT of all these "rare" elements. Some of them are in the 20th spot by % of the Earth's composition. However they're really "rare" in that they tend to not clump in veins or ore deposits that are very economical to mine, because of molten circulation during planetary formation, continental drift or whatever has distributed them very evenly, or just too deeply to access.
The Asteroids, either never having formed into a body in the first place due to tidal forces and gravitational disruptions from the other early planets and Jupiter, or been blasted apart out of the cores of colliding protoplanets or larger asteroids, the concentrations of these metals are many times higher in some asteroids, sometimes orders of magnitude higher than they're found at any accessible depth of Earth's crust. The Iridium layer from the KT impactor alone proves it, even if it hadn't already been confirmed by some of our space probe's spectroscopy.
In theory even the carbonaceous chondrites are valuable, because the carbon, hydrogen/oxygen/water bound up in them and any lighter silicates are still very inexpensive in terms of fuel and Delta-V energy or transport costs as compared to stuff that's down the gravity well on a planet. Although after a certain amount of "living off the land" to fuel, support, and supply asteroid mining for the rare metals, them being useful further than that presupposes other space settlements, bases, or infrastructure that can use it.
I'd guess that ingots of rare metals could be slung on low energy trajectories wrapped in heat shields made of foamed slag for splashdown in the ocean. At least that's how I'd look into doing it. Asteroid water or hydrogen/oxygen would only make economic sense to other microgravity locations. Even the moon probably has enough that can be mined locally that sending/setting it down is not economical.
