R4 gba emulator not possible?

i have looked everywhere and from what I can tell, nobody has made gba emulator software for the NDS. I see second slot cards but that's stupid. can somebody please explain to me why this is not possible because I believe it is possible, its just nobody has bothered to do it. Reason why I say this is because we have so many other emulators on the r4 like lameboy or jenesis so why is there not one for the gba?

because the DS isn't powerful enough to emulate GBA.slot 2 works because the slot is connected directly to actual GBA hardware.