After reflection I think Brook has taken a number of factors into account when he's taken the knee.
His previous injury and the warnings he would have been given about losing his sight etc.
Not wanting to be sparkled out licking the canvas in his hometown stadium.
Knowing he wasn't going to win on points and had blown his gasket the round before.
I don't agree with Kirk's comments about not letting a boxer quit, that's just fucking stupid and shows real contempt for how much danger they put themselves in when they go into the ring. It's their life and they should be in control of it. Brook gave that crowd a fantastic fight, it's up to him if he wants to take a knee.