Brook has been played, all he can think about is the Khan fight while Khan himself has gone to do well for himself. Brook can’t get motivated for anyone else but Khan because it’s a good pay day where he won’t get hurt.
His ego won't allow him to do so because, as some have already pointed out, Brook knows a fight with Khan is his biggest payday.
The brook - Khan situation reminds one of the Khan- Floyd situation. Khan seems to get big paydays no matter what he does or who he fights. Khan is getting far more pleasure out of making brook wait about than the pleasure he will get from the brook payday. Brook needs to forget all about Khan and get on with his career or just simply retire