He was getting pieced up and realised this wasn't a feather fisted flabby dosser with papier mache skin he was in against. Smart man.
He was taking a pulping. Even the blocked punches were doing him damage. He was going to be ko'd in the next few rounds. Don't think he expected Joshua to be that sharp , accurate and powerful. No doubt he's learned a thing or two about fighting southpaws from the Usyk losses. He looked really good.
Simple > levels. Though it's funny as all i have heard all fight week, was Wallin was never been stop before, Walling was durable asf, Wallin has never ever been dropped before, and that AJ can't fight lefties .... Oh yeah and how could i have forget, that Wallin will outbox AJ, and judges will rob him .... Wallin was top 10 in every HW Ranking, Number 2 in the IBF, but he was bang average. Boxing is about style, and Wallin style wise for guys like AJ, Dubois, etc. is literally perfect.
Because he knew it was over and AJ was just on a different level. Probably a smart decision to prevent a brutal stoppage.
He shouldn't get another big fight after that. Seems like there's more real fighting men in MMA than boxing nowadays. If someone did that in the UFC they'd be getting slaughtered.
Rematch it and you notice from about 30 seconds into the 5th round his face starts draining of colour and his whole head goes white.