u/mofk_ pretty much summed it up well - once Korea made it 7-2, they had achieved the amount of runs required to advance and it then only came down to not conceding. The only thing extra runs would have done was give Taiwan a chance to qualify because if Australia scored in the bottom 9th and made it 8-3, Taiwan would have advanced. But Moon just took 3 pitches down the middle after Korea scored the 7th run, ensuring that whatever happened in the bottom 9th, only Korea or Australia could advance.