Why? HBM2 is not DDR4. There is no spot market I can identify for it. The supply metrics appear to be completely different.
This is because the electronics industry is in a downturn. This is particularly apparent for the graphic card market.
Year on year, there has been a 40% reduction in graphic sales compared to last year. Even worse than what has been happening in the PC and mobile market as far as declines go.
So what happens when demand falls? Prices fall, particularly in the memory market. HBM2 was initially overpriced because money and production were going towards things like mobile market, traditional DDR4 and even regular gddr5. There were prices increase across the board because demand exceeded supply and this was true of HBM2. With declines in videocard sales and data center sales, Vega in particular and the opportunity cost to make HBM2 instead of DDR4 way down now, HBM2 has an over supply issue now along with the rest of the memory industry.
HBM2 can be made cheap if we look at HBM1 prices which was indicated to be 35 dollars for 4gb. HBM2 was initially really expensive initially because the first customer for it was Nvidia who were putting it into graphics cards 10k which means they didn't care about the component cost as much and on top of this, they demanded Terabytes of the stuff. This created initially artificially high prices, where suppliers could charge somewhere along the lines of 2x-2.5x premium over HBM1. On top of this, Hynix was the only maker at the time. So combine low supply and heavy demand and what do you get? High prices.
So why did they stay high? Nvidia data center market was expanding rapidly(kept growing quarterly) and as a result, Nvidia was swallowing everything up with big super computing contracts(which have since been completed) where they could afford the high prices of HBM2 no matter how much the price increased. This puts a huge strain on demand. What compounded on this was Vega. Vega was the first consumer product with HBM2 on it. This along with the data center industry, increased demand even with ramp ups and samsung entering the mix. See a theme here about supply and demand yet?
So what happens when demand falls because the data center market is finally showing signs of slowing and Vega demand falls off a cliff, along with the rest of the graphic industry. Demand falls, which effect suppliers where they finally have to lower their prices. Particularly now since the entire memory market is affected from cell phones, to ram, to graphics cards to SSDs, it is not a matter of shifting production from one area to the next profitable one, prices have to fall everywhere.
HBM2 is not in some sort of magical bubbles that prevents them from being effect from the laws of supply and demand. Look at the prices of RX Vega and it is clear the demand for the card is low now. So what does this cause to happen, demand is low on HBM2, which in turn lowers pricing on it. So along with the increase in supply factors I mentioned earlier(ramp ups, production, samsung getting into the mix) and the price Vega is currently selling it, there is absolutely no way HBM2 pricing is the same now as compared to when Vega is released. How do we know this for certain?
Look at the price of Vega now compared to Vega when it launched and shortly after. It is about 150-200 dollars cheaper. So how is such a price cut possible? The answer is a fall in pricing of HBM2. HBM2 prices has to have fallen because the demand strain is simply not enough to sustain that 150 dollar price tag and it is the biggest portion of the bill of materials where a price cut is possible.