Their respective backgrounds and experiences. Thrall experienced his childhood and teenage years training to be an Blackmoore gladiator. The rest of his life was spent fighting. After escaping, he led the fight against Durnholde that WOW TBC Gold involved numerous combats and raids on the forces of Lordaeron. As a quick aside of sorts, the "Lords of the Clans" were very open about Thrall's height as compared to ordinary orcs did not stop talking. Soon after his victory, he was able to win the third war. It was a conflict where the fate of the entire world was in the balance. In the end, he was able to lead his people to victory alongside the night elves , as well as the human race. Then, even more quickly they saw the Daelin took over Durotar which prompted Thrall and his men to fight in war again. My point is Thrall was a soldier and trained for most of his life. There were some lapses of times when he didn't like vanilla WoW or the birth of Durotar. His life was full of battles and more than anything.
Garrosh, on his own, has very little experience and no training to draw upon. He was raised in isolation, with no major foe or conflict that could give him strength. Since the tribe of ogres had moved to Nagrand only recently after the Bladespire gained control of their territories in the north. He was obviously given an education, given that it is orc culture to fight and hunt for a living, but it's just an implied fact and not something to note. He doesn't spend any time in TBC fighting the Legion or Illidan. Wrath is the sole instance where it is possible to argue that he was properly prepared and exposed to the war against the Scourge. However, even this is largely in connection with the fact that he never ever did anything during the entire expansion. And as much as a legend Saurfang is, his training Garrosh for 2 years at the buy WOW TBC Classic Gold very most will not be enough to replace many years of war. He did not participate in any major Cataclysm conflict. Like the majority of MoP with the sole major battle that he was involved in was his death during the siege of Ogrimmar.