That is gun deaths, not gun homicides or mass shootings. Around 2/3rds of gun deaths are suicides. A suicidal person will choose the most effective and painless method available to them, so if they have a gun around, they'll use it. This is a totally different problem than gun violence, but many activists will conflate the two.

Because they are sneaking suicides into the numbers. If you split the data up between suicides and homicides, the correlation disappears.