Why do my bone grafts keep failing?

Had #3 and #13 pulled 12 years ago. Bone loss was more severe on #3. Cadaver block grafts done initially. Both failed. Round 2 we did granulated cadaver none mixed with my own blood. #3 fails. Dooctor says since tooth #2 has some root exposed and a filling the graft doesnt want to attach so hes trying to bulk up around it. Is this common?