I thought this was done out of morbid curiosity. The 3DS version is superior in every way. More pixels, higher polygon count, cleaner sharper textures, more/better/accurate effects, shaders, lack of PS2 blur, no green filter. Not to mention rendered at a full 60FPS at a higher res or 30FPS in 3D mode plus the additional calculations required for 3D mode, things this video can't show.
It's all very subtle due to design and cost. It's not cost effective to redo every texture, every model, every effect. They are going to prioritise getting a smooth, working bug-free game out over a complete rebuild of every single aspect.