In terms of the game mechanics behind it...
Commodities with heavy state table dependence will look volatile on the metric you're using, regardless of whether they're "desirable" or heavily used by players.
- Primarily, very different state tables. Platinum and Osmium prices are especially boosted by Boom, which is very commonplace, and not much else. So the top end of the market is all in Boom, all with similar prices. Painite and LTDs are boosted moderately by several different states, with Painite additionally boosted heavily by Public Holiday or Pirate Attacks - states which can only last a couple of days. LTDs best major combination seems to be Boom+Expansion - rarer than just Boom, but still common galaxy-wide - with Pirate Attack helping a bit.
- Secondarily, Platinum has ten times the demand of Painite/LTDs, Osmium has ten times the demand of Platinum. That means all else roughly equal, 10x and 100x faster demand regeneration for Platinum and Osmium. So even if most people aren't mining Painite, there won't be 100x as many people mining Osmium. Because of the above state table differences the Osmium/Platinum sales will be more spread out, and the LTD sales will still be more spread out than the Painite
Ceramic Composites now: Cr5,445-Cr10,515. Spread of 93%
Ceramic Composites on a good day where its super-state combination exists anywhere: Cr 5,445-Cr27,000. Spread of 496%
...even more basic goods than that:
Power Generators: Cr3,649-Cr4,492 (23%)
Water Purifiers: Cr3,060-Cr4,628 (51%)
So, the volatility [1] you're looking at is basically "does the top state combination occur at >25 stations at once, or <25 stations at once"
Having some goods with reliable prices, and some goods which are occasionally a bit better but usually lower, is needed to make the markets interesting - the trade side of things has had plenty of examples of this for a while now.
[1] One issue of the "spread" metric is that on days where the super-rare combination doesn't occur at all, the spread looks lower despite the good actually being even more volatile, as in the Ceramic Composites example. (It's possible that this is also why LTDs look so low, not sure)
In terms of in-universe logic [2], Osmium and Platinum are valuable commodities with important industrial and technological uses, so they behave similarly to the other cheaper metals, with mainly economic states boosting the price.
Painite is a gemstone useful only for decoration, so it behaves similarly to the core-only gems with mainly event states boosting the price. As the Painite market has famously been a bit saturated, it's "last season's" gem and so less valuable than the others, though.
[2] Which is deteriorating rapidly as far as the relative prices of trade goods goes. Non-minable goods pricing is now a complete mess. But that's a separate complaint...
That's mostly plausible, but I feel like the comparison with LTDs shows that Painite IS out of whack.
I guess we could justify it by suggesting that LTDs have some kind of industrial/technological purpose that stabilises their market but that's a bit contrived.