Why did Majitani's surrender not count in his Trick Tower fight with Kurapika?
I don't know about the anime, but in the manga, Bendot explicitly said, they would fight until one of them surrenders or dies.

In Kurapikkas fight they agreed to fight to the death. The rest is as you said. He wasn't dead, so the fight was not over. But Kurapika heard the surrender of Majitani, so he refused to kill him.