It was the whole Captain Universe thing that pissed Cytorrak off. Cain got depowered before, then got his full powers back when he fought WWH and then fought Skaar afterward.
After that though, the guy whose life he'd ruined when he fought Spider-Man that first time got the Uni-Power and went after him. He used the power for revenge though and the power transferred to Cain who became Cap Universe and was charged with fixing the tunnel he dug from the construction site to the East River to get out of the concrete.
I don't remember the issue or exactly what he said, but long story short, Cytorrak got really pissed at him and depowered him again. How weak he was was really inconsistent though. As at some point he got burned and other weak stuff, but then he took it to Cage and Thor and King Hyperion.