N64 emulation is actually "easier" than PS2 emulation in terms of performance. All the N64 emulators out there are high level emulation. Meaning, they don't try to copy the original hardware. They simply take the commands (like how to draw a rectangle) and perform the PC equivalent. Since the N64 was most 3D polygon gaming, this was acceptable. High level emulation means better performance but lesser compatibility. You could get great N64 performance back in the days of 3dfx.
All the PS2 emulators are traditional emulators and they try to copy the PS2 hardware exactly so the demand for good hardware is higher.
As far as the games themselves, it's far easier and cheaper to just download the illegal images. Ripping your own games requires a monetary investment and time on your part.