Because it was indeed like that: Garp was giving it all and Kuzan was far from it, and Garp himself pointed that out.
Also, Garp barely gave some hit to Kuzan, and he returned shortly after.
Also, Garp barely gave some hit to Kuzan, and he returned shortly after.
Garp was pointing out that Kuzan has become conflicted not that he wasn't trying buddy!
Shiryu got in the way before Garp could beat Kuzan, the manga makes it clear that if not for Shiryu they wouldn't have beaten iron Garp