Right wing paranoia is surely part of the explanation

Gun inequality: US study charts rise of hardcore super owners | US news | The Guardian

New survey, part of most definitive portrait of gun ownership in
decades, shows just 3% of American adults own half of guns in the US.

Good news, I guess, is that the percentage of owners (per population) overall has dropped a little.  Bad news:  some of the remaining owners are massively paranoid.