A 40 lb weight advantage isn't enough? He was fighting somebody who's already faster than him with better footwork, so he came in better shape to minimize the speed difference while still keeping a huge size advantage.
He comes in heavy against KO punchers so he can lean on them to make their arms heavy to take away their power. He was like 253 or something in the 1st Wilder fight and Wilder still nearly killed him in the 12th round, so he changed it up and came in way heavier for the next 2 so he could clinch and wear him out. He was in the 260s against Whyte and Chisora.
His 2 strategies would have been to lean on him and wear him out, or to use his huge height advantage to keep distance and make him have to reach, and catch him with uppercuts when he does. He picked the 2nd because Usyk isn't a power puncher anyway, and it seemed to be working when he got the timing, and looked like he could run away with it until Usyk made the adjustments. It's questionable whether coming in fatter and leaning instead would have been better.