Might be due to their highly restrictive laws.
Due to those highly restrictive laws, knives are now the Weapon de Jour in most violent crimes.
Problem solved, 'eh?.
If you ban all guns, root out said guns, destroy said guns and stop the smuggling in and manufacture of guns, then you would solve the problem. But that's impossible.
So what sensible governments do, they licence guns and regulate the types allowable by law, same as cars as an example. What these do, they reduce incidents. If they miraculously eradicate the problem, amazing, but that will never happen. So be it knives, baseball Bats, guns etc.. all you can do is regulate where possible to reduce incidents where possible, and the type of incidents influences these regulations/laws.
But to say, "Ah, look at that, a car crash. That's it, scrap all regulations". Or, "Ah, look at that gun incident, scrap all regulations", never heard anything as stupid as that.
If America was at all interested in gun lives, the Senators would do something about it, but they're not interested. So you enjoy high gun deaths and gun violence.
If you're interested in knife crime -
How likely is it that offenders will be sent to jail - and how long do they spend behind bars?
www.bbc.co.uk
The minimum sentence for possession of a gun is 5 years.