In California, this is absolutely not the case. Regulations are strict, chemical emissions are heavily restricted and proper disposal of chemicals via specialized companies at great expense. Chemical companies have no need of formulating new versions because everything causes cancer under prop 65. They absolutely have numerous permits for chemicals, your claim that they don't denies reality.
This case probably fell through the cracks, was grandfathered in due to military importance, or is a symptom of the utter lack of industrial knowhow plaguing modern US manufacturing because much US manufacturing is legacy work from decades ago with little ability to modernize, at a plant that likely existing long before the nearby housing.
That's the deep dive that I want to see. A breakdown of the policy failures that lead to this situation.
Why is a tank this large of a chemical that can have runaway thermal reaction allowed in an area 500ft from residential areas? Why is this chemical allowed in an area that is considered light manufacturing?
The plant was built after the houses but likely well before we had anything resembling modern safety regulations regarding such things. It was presumably grandfathered in for no reason other than that arbitrarily putting someone out of business after the fact is generally frowned upon. https://news.ycombinator.com/item?id=48254291
That company (GKN Aerospace) was recently fined $900k by California for various violations dating to 2020 (including instances of incomplete records and missing permits). To be clear my intent isn't to single them out. I cynically assume at least some amount of that behavior to be par for the course with US chemical companies.