Since gun ownership and the number of guns have both been rising continuously for years, you can correlate them to anything you like. Since the number of guns was over three hundred million when the murder rate was lower, we can also correlate a large number of guns in circulation to lower murder rates. Or rising rates, or dropping rates. No matter where the trend moves, as long as there are over three hundred million guns in the US, guns are basically as available as milk and gasoline and effectively a constant. Or do you honestly believe going from three hundred million guns to three hundred and one million guns is worthy of measure for correlation?

All of this is irrelevant in any case. 99.95% of guns are benign in the US. This isn't conjecture - its a clear ratio of total guns in circulation vs gun homicides. A law-abiding owner of a gun should be as concerned by a gun used in a murder as a chef would be concerned about someone being stabbed with a pearing knife.

If you want a more realistic answer, I would suggest both economic desperation (unemployment, inequality, need) and pressures due to a new and unnatural mode of living enforced on the population (lockdown). Or if you want to get political, all of the cities in the infographic are blue cities that moved to lax policing policies in 2020.