https://www.washingtonpost.com/news/morning-mix/wp/2014/08/1...
Full metal jackets are required for war, while law enforcement use bullets for stopping power.
One way the U.S. could reduce gun deaths would be to require full metal jacket ammunition; It decreases the likelihood of death for any given hit; (though increases ricochets and likelihood of stray bullets)(also increases price of every bullet sold)
That being said, there has been a lot of evidence that shows that HP rounds penetrate further than conventional wisdom would expect, and it likely gives LEOs a false sense of security when firing in an apartment complex or into crowds.
I suspect that this is more true of the public justification for their use than the motivation (not saying it's not part of both, though.) Politically, “it reduces risk of accidental injury to bystanders” is probably more palatable, especially to the factions most likely to object to police-preferred gear, etc., than “it makes the injuries to the people we target more grievous”.