Because a peak David Haye is an underrated fighter. And that underrated fighter fought in a way that just about ensured he wouldnt be caught.
Haye didn't employ a high guard as most of Vlad's opponents chose to use which let him see the punches coming and because he was light and fast for the division he was able to roll with them effectively. Because of this, I don't really recall him being hit clean too often. Also, he and Booth came up with the awkward-to-watch plan of falling over when Vlad tried to lean on him and tire him out, but I think this was effective if slightly embarrassing. However, more importantly than all this, the searing pain from his toe made him impervious to pain anywhere else...
Bellew answered this during the Haye-Bellew I build up. Haye said there is no way Bellew could hurt him, since Wlad was unable to do so. Bellew said something alike “Because you will go in there on the front foot, trying to tear my head off. Against Wlad you were on the back foot and didn’t engage him at all.”
Haye has always been pretty elusive, his head and upper body movement means he isn't easy to hit clean. That along with Wlad's cautious style and nature he wasn't ever going to press Haye and Haye being a natural counter puncher was never going to press the action and force a stoppage either.
If you watch the face off interview between the two it was obvious Haye knew he couldnt win, he was nervous and talking nonsense whilst Klitschko was relaxed and confident.
I see some only remember what you want to remember. And not answering the question of the TC . Instead i see much deflection from Wlad and focusing on what Haye did or did not do. Haye did threaten Wlad with promises of knocking him out . But Wlad promised he would turn Haye into a " pizza face" . Yep Wlad insisted he was going tear Haye's face up so much so that his face would resemble a pizza with its red sauce ( blood ) all over his face ( cheese) . But Wlad did no such thing. Fought negative , pushed Haye down repeatedly and fought to survive.
Because Wlad is a safety first fighter, and he might have been KOed. Haye rocked Wlad in the 12th with the only meaningful punch he landed in the whole fight.