Large animals like Godzilla cannot exist on land because their body weight increases faster than the strength of their limbs can support, causing them to collapse.

“So as you get bigger yeah your volume grows I your weight goes up according to your volume yeah what the strength of your limbs goes up only according to this cross-sectional area so it's a matter of area versus volume some Villa is Godzilla collapse under the weight into a puddle of guts”