Probably the price and the desire to own the Proof. Just about all the proof ASEs, including the most minted, are selling for around $55. Now if you sent one to a TSP and it came back PF70, that's a different story. So far, PCGS has graded 535, 2010 Proof ASEs PF70. Their value, as per the PCGS POP Report, only $85.
ebay has them listed any where from $42 to $175 depending on the grade. Even the 1986 proof, the highest number minted at 1.44 million (and excluding the 94, 95, and 06 issues) is higher than the rest at an
average price over $102. Numismedia is much more realistic with valuing them in the high $40 to $80 range for DCAM coins. I should add that Numismedia has the PF70 DCAM valued at $750.
I know.....it's just a bullion coin but it's always what the market will bear. Some people go crazy for MS/PF70 coins.
"Hey, it's their money, and they'll use it as they see fit."