I have no idea how both HW works, but i guess that if Nintendo cut back on some textures or something they could easily put the same number of Pikmin and enemies on screen.
Textures and geometry is gpu work, The 3ds has a pretty dang good gpu, good enough to exceed the wii in many areas. It can likely draw plenty of pikmin no problem.
The problem is controlling them, their ai, would be too much for an arm 11 and its vfpu to handle.
You would have to 'billboard' (attach many characters to a single ai routines movements, theyd all move at the exact same time in the exact same direction) which would degrade the pathfinding, and behavior, and thus horribly break the games dextrous control over large groups of pikmin.
During many parts of pikmin, each individual pikmin was controlled by its own ai, and compared to other strategy games billboarding was kept to a minimum, its what made pikmin, pikmin, and set it apart from other rts's.
Without it, pikmin would just be a simplistic ant themed command and conquer, which is likely exactly what mr. miyamoto didnt li,e about the gba and 3ds attempts.
