That's possible, but I think it's more because the people who assemble the statistics don't count it until a certain number of people are shot. It actually _does_ happen that occasionally someone will try to shoot a bunch of people in a public place where people _are_ allowed to defend themselves, but when that happens they're stopped before they can kill enough people for it to count as a "mass shooting." For example, there was an incident just recently in a mall in Oregon where some nut started shooting, but after hitting two people he saw that one of the mall-goers had drawn a pistol and was aiming at him, at which point he shot himself--so it doesn't count. Naturally, those events don't get even remotely as much coverage, as they don't satisfy the mass media's bloodlust or political agendas.
And of course, you're still in more danger of being struck by lightning.
And of course, you're still in more danger of being struck by lightning.