Sauerland didn't want the fight at the time. Chagaev beat Valuev and took his belt anyway, and Wlad beat Chagaev.
Vitali was being lined up for him rather than Wlad. Valuev claims that there were two rematch clauses in case he should beat Vitali twice he should then fight Wlad. He didn't want to be tied up for those three fights and said "no thanks." Not sure it's true, but that is what Vaulev claims.
Wlad didn't use jab and grab tactics against bigger guys and he didn't need to - watch Mariusz Wach fight Wlad would dominate Valuev and eventually KO him
Valuev would not be able to cope with Wlad's power, Wlad was stronger and would completely demolish him...
Aside from his many controversial decision wins, Valuev lost to Chagaev and Haye, who both went on to get dominated by Wlad. Valuev couldn't cut it at championship level.
How many leaping left hooks do you think Valuev could take in a row? I say this because he would be too slow and open to defend against it.
Valuev shew a chicken dance with a Cruiser like Haye. He would get completely rocked by a series of Wlad right hands.