There are many variables, but the simple answer is easy enough to come by: they did fantastic as early-market entrants into the asic market. In the summer they were sustaining mining rates over 10% steadily and sold ample hardware.
But things go quick in BTC world. So a few months later, many new companies came to market with asics, some backed by big money and or significant expertise. Asicminer resultingly lost market share for their products. They are sort of repositioning themselves in the market, it remains to be seen if they will ever be able to regain the foothold they had.
Personally I think the company will continue to innovate, increase production, and sell a popular product at market rates, and go up in share price. But having said that, Asicminer will unlikely ever have such dominance and relevance as they understandably did when their was only 3 players in town (+Avalon, +BFL).
Who are the new players? I know knc miner out of sweden, who else?