Russia is an even smaller economy than the US, and even then many countries continue to trade with them despite their aggression.

Sanctions hurt everyone involved. If China stopped trading with the US, their economy would tank too.

Furthermore, there are ways around sanctions.

The US is much more self-sufficient than Russia.

It is not hard to comprehend, but it is also not a surefire way to deter an invasion.

And of course remember that not all actors on the stage will behave "rationally"... US leadership especially.

If the US were in this position, any country that had sanctions that were only there at the urging from the US would be dropped. Even if they were not dropped, those that were sanctioned would immediately start ignoring them. Hell, most of Europe would probably immediately starting buying oil/gas from Russia.

if the world was going to cut trade with the US, it would have over the iraq invasion.