It’s because she’s an earthbender.
Airbenders change their approach to solve problems. If one approach isn’t working, they do another one. Aang constantly does this, in the show, he doesn’t want to kill Ozai, so he just goes out of his way to find another option to killing him.
Show an airbender a mountain, and they’ll use their air bending let them go around it.
Waterbenders change themselves to solve problems. If their approach isn’t working, they change themselves to best solve it. Korra was exceptional at bending earth, fire, and water, because she was good at changing herself to use different elements. Her only trouble was air, but by the end of the first season or so, she had changed herself to use it properly and used that change to help her take down the equalists.
Show a waterbender a mountain, and they’ll use their water bending to help them create the best path up the mountain, and then use it to best go down the mountain once their reach the summit.
Firebenders change their emotions to to solve problems. If their approach isn’t working, they get passionate enough to change it. That’s Roku’s strength. He never had a problem with the power to stop Sozin, he just had to work up the passion to do so.
Show a firebender a mountain and they’ll rage, and rage, and rage, until they get passionate enough to burn their way over the mountain.
And then there’s earthbenders.
Earthbenders don’t change anything to solve problems. If people tell them their approach won’t work, Earthbenders take a stance, plant their feet, and do it anyway.
Because it takes a certain type of people to slam their hands into rocks daily. And that requires a will and conviction strong enough, that when they are shown the biggest, baddest mountain on earth, they don’t go around it, they don’t flow over it, they don’t burn up it. All they do, is take a stance, plant their feet, and whisper…
And should the earthbender prove strong enough, and their will powerful enough, the mountain whispers back.
Kyoshi wasn’t strong because she was an avatar.
Kyoshi was strong because she was an earthbender, through and through, with the sheer frigging balls to tell the world to move.
And she said it with enough force, the world listened.
