Here are a few plausible answers...
The tea was initially overpriced. If the tea was initially overpriced when it was first put on the market or was over priced for years and year and marketed as high end puerh without the material to back it up, then you would expect there to be a lot left over. Think about it, if you are selling a product that you know will only increase in price why not over price it and see how much you can sell and what you don’t sell you can likely sell later for much more years later. This is the reality of selling puerh. The only problem is when the tea reaches a celling price where the market will no longer pay much more and the tea no longer increases exponentially in value annually. I think the owners of YangQingHao are at this point in the market for 2004-2011 puerh and so they have incentive to sell now and keep prices relatively stable.
Personally, back in the mid-2000s I did not have the appetite to spend $135.00 on puerh. This tea was marketed to a very niche group of puerh drinkers and, at the time, many thought it was a bit overpriced. What is most interesting to me is that the price of this tea has not increased 10X the initial price like some of the factory puerh from that time period (i.e. Douji, Chen Shang Hao, ect). The price of Yang Qing Hao has only modestly gone up since that time.
The centralized supply management of Yang Qing Yao. Another plausible reason there are many Yang Qing Hao cakes is that the market supply has been closely monitored and controlled by Mr. Yang. I don't think he was selling this tea by the jian to warehouses and distributors and other vendors. This really allowed for market control of the price, I suspect.
Export duties from Mainland China. I really don't know enough about this. I wonder if this operation was on the Mainland would more of the inventory be long gone?
Large production size. Sha8 had mentioned this before somewhere. He suspects that Yang may have had access to giant swaths of tea gardens all to himself. He also suspects that production numbers for these cakes are much higher than most boutique Puerh especially compared to the scale of production these days.
In the next few weeks and months I hope to explore the question of whether or not Yang Qing Hao is worth the money by posting notes on a few of these productions. Even though there is tones written about Yang Qing Hao, I hope to try and add a new, fresh, personal perspective on these frequently reviewed puerh. Please join me in this exercise as I meditate with Yang Qing Hao.