My belief is that Thrall was unable to WOW TBC Gold use his abilities and allowed them to go in favour of his shamanistic talents. Garrosh's genetics and skill are also reasons why Garrosh was able to win until Thrall invoked elements.
Thrall does not know the reason he's fighting. He is not fighting Garrosh to make Garrosh realize his mistake or to make him kill him. Instead, he's fighting Garrosh because he feels guilty. Garrosh however knows what he's fighting which is to get rid cheap WOW Classic TBC Gold of Thrall. Garrosh is kicked by Thrall until Thrall realizes there is no way to save him and that Garrosh must be taken care of.