I don't understand what you mean by "sustainable". The whole industry tripled their process AND is maxing out their production lines. They are cashing out as expected.
It matters nothing if this trend can't be kept up for years, because by then their output still meets demand AND they will be sitting on a huge bag of cash.
I think you are confusing "I don't want to pay this much" with "this isn't sustainable". The sellers are cleaning up stock at a huge markup and buyers are still buying like crazy.