One can think of an explosion causing a roughly spherical shockwave. For a ground level explosion there's a relatively narrow "band" of that shockwave that trav

One can think of an explosion causing a roughly spherical shockwave. For a ground level explosion there's a relatively narrow "band" of that shockwave that travels along the surface of the earth damaging buildings and other stuff, the rest is either directed upwards, or as you say, to create a crater (and a lot of the "cratering energy" will be reflected upwards towards the sky as well). A ground level explosion also means that nearby buildings and geography (hills etc.) shield things behind them, reducing the destructive effect. With an airburst you have a more even distribution of destructive energy over a larger area.