1) Basically it's a chemical by-product of an unrelated manufacturing process.
2) Either the chemical itself, or the process that creates it as a by product (or both) were banned in some countries several years back (which caused a TC tire scare then as well - earlier in this thread a magazine article about that was quoted).
3) A global ban was initiated a couple of years ago, which had anyone manufacturing rubber products with similar characteristics of our tires (long wear, pliable, and high grip) in a desperate search for an alternative. I've spoken to such folks personally, and the replacement chemical that works for them isn't quite as good, but it still works acceptably for them.
4) So it didn't just get "expensive" - it just was no longer made - period.
So Jason - why is it so important for you to know the name of this magic chemical that is no longer in production/in use? We're talking about events that happened almost 2 yrs ago now