Thisbecause kisame died after kabuto had finnished Getting the DNA.
this is the most logical reason.Because his DNA is inside his sharks stomach.
kabuto must be very diligent to obtain the weapons of the former/edo 7 swordsmen of the mist.Even Kabuto gets his hand on Kisame's dna, I read somewhere edo tensei cant revive the special weapons like samehada. Kisame will be not as powerful without it.
Because his DNA is inside his sharks stomach.
These.because kisame died after kabuto had finnished Getting the DNA.