Just quickly skimming through the Icons.LOD...We have four female variations (GirlA through GirlD) and eight male variations (MaleA through MaleH). Each one has 53 expressions... not quite as much as in 7 or 8, but still quite a few. Moreover, everyone has a paper doll, a character creation face (essentially just a copy of the normal expression in a window frame), and two arm graphics (for 1-handed/2-handed weapons).
53 faces would be a lot of drawing! We could import portraits from 7 or 8... these would work well, EXCEPT for the paper doll in the inventory. This is of course because different poses are used in the inventory in every game, so someone would have to redraw the character from 7 or 8 standing in the MM6 inventory pose. (Or just resign ourselves to looking at a complete stranger every time we open the character menu!)