Observation bias.
300+ million people. There are X% of people shot every year, regardless of population level. If X = 0.01% (way higher than reality but I don't know the real number), then when population is 50 million, it's 5000 people a year. When the population is 300 million, it's 30,000 people.
Now introduce internet, cell phone cameras, rapid response news teams, and news cycles that react to consumer paranoia on particular topics. We hear about EVERY shooting right now. Seriously, who didn't think that at least a dozen people were shot in Chicago just about every night? There's well over 500 murders a year there, on average, and most shootings (well over 80%, isn't it?) don't result in death. There's probably somewhere around 5000 shootings every year just in Chicago.