[smileysteve]

Presumably, the regulation had reasoning. Likely unsightfulness. But also likely danger.

Will the port's insurer cover damages when a 3 or 4 high stack falls?

[booleangate]

Unsightliness maybe, but also California is no stranger to earthquakes. Stacking up to 6 high sounds like a deadly and expensive game of dominos.

[KptMarchewa]

They can be stacked higher on a container ship when full. And ships are subjected to what someone could think of as a "quake" - waves.

[eecc]

for sure, but the harmonic characteristics of sea waves are rather different.

But yeah, you do have a point.