It's the same reason this sort of thing caused the market to crash in the first place. Yes, you had lot's of people buying these comics with the notion that it would increase in price down the line. But those weren't fans following along because of the story. They were one off investors who were just showing up to pick up the latest issue as an investment for a later sale down the line. They were artificially inflating the market with their purchases. And since they weren't really all that concerned with the comic, they could take or leave it. Which they did when the bubble burst and they found that a lot of other people had the exact comics they had and the "investment" they though were going to pay for their retirements in a few years were now worthless. So the retaillers had no reason to keep buying these multiple copies for the casual investor who would be willing to pay for two or three extra copies of the comic, and now had to service those fans who were only willing to buy a single copy. And that deflated the market quite a bit.
The long of the short of it is, it's proven to be a VERY short lived strategy that can have VERY negative long term repercussions on the marketplace.