Mosley always had stiff hips. Almost every time he's ever been hurt in boxing (and he was still very difficult to hurt despite this), you can see his stiffness immediately after being hurt:
His hips just aren't and never were flexible. At lighter weights, where no one was strong enough to hurt him, it didn't matter. But it sure came into effect later. And it interrupted his ability to defend himself.
In fact you can SEE hip-mobility playing a factor in that fight when Canelo would land. He'd take an angle using his own more flexible hips, Shane wouldn't move, and he'd fire. If Shane's speed and power didn't keep you at bay, or you could neutralize it, you could use his lack of ability to change positions against him. In his younger days he relied solely on his legs, stepping in and out.
Contrast that to Marquez whose ability to use his flexible hips when he's hurt almost always got him out of trouble and led to KO's:
He was never the "cover up and hope the other guy leaves you alone" kind of fighter. He was more of a "take an angle and hit the guy back harder than he hit you" guy.
