What would happen if you scaled an ant up to the size of an elephant? Its legs would become thicker in the same proportion, but its weight would increase much faster, eventually making its own legs unable to support it. Increase the size with the slider and see the effect for yourself.
Key idea: If you scale length by k, surface area (length × length) becomes k² times larger, while volume (length × length × length) becomes k³ times larger. As k increases, volume grows much faster than surface area — this is why the legs of large animals need to be proportionally much thicker (the leg cross-sectional area must support body weight, which is proportional to volume).