You need to understand that the resolution of the shadow map will stay the same regardless of the settings you set for the light shadow settings. If you increase the distance you’re effectively stretching the shadow map, which in turn causes low res shadows.
Cascaded shadow maps just split that single shadow map into different parts and those parts can be made larger or smaller depending on your settings. It basically allows you to trade resolution between far and near cascades. Far away stuff doesn’t require much resolution since you can’t see it anyway, so it’s better to use that resolution close to the camera.