You might not need (say) 100 firefighters for the day to day work in a medium city any more... but you absolutely need 100 firefighters when the large chemical plant goes up in a blaze.

It's hard enough in Germany to balance that, but we at least can draw on the advantage of Germany being decently settled which means we can have support crews come in from neighboring cities. But in the US where it might be the case that the nearest city with enough staff is hours of driving away? By the time you get enough staff on site, the entire plant is gone.

That is not how the US looks/works. The large chemical plant is in a large city (or suburb) where they can call plenty of other nearby cities for help.

Most of the land in the US doesn't have enough population to support a large chemical plant. The plant needs not only the people who work in the plant. It also needs schools, grocery stores, libraries, doctors... And that many people also really want things like sports teams. A small chemical plant can locate in a rural areas, but not a large one.