What happened between Q2 2014 and Q3 2014 to make them lose nearly 10%?
Like Halfmad and elmuzzy66 said I would guess that it was the end of the mining craze which was keeping AMD's market share artificially high, that would have been the ideal time for AMD to release a new range of cards but since they haven't AMD owners have had no reason to upgrade and for those in the market Maxwell based cards could be seen as much more attractive?