The main problem is American culture and unfortunately also with the way their political system works.
Back when I lived in the US, the thing which struck me the most was how law abiding and respectful to the law most people were. Yes there are random shootings but we also have to realise the country is simply HUGE. In general I felt way safer over there than in the UK.
But at the same time some of their ways of thinking seem alien to us. So many of them believe and continue to believe that this tragedy would have been sorted quicker if everyone had guns. I doubt you would find many Europeans believing the same.
Guns are a way of life for many American's. I remember a guy I was working with. To him going hunting at the weekend with his rifle and guns was as normal as someone in the UK taking a fishing rod to his local lake. He taught his daughter how to use guns at the age of 10. To him the idea of gun control was simply correct handling of a weapon. And the idea of the government banning the public using guns was as repugnant as our government banning fishing rods.
It's simply telling that after the shooting of so many people that neither presidential candidates have said anything about gun control.