Same reason USA has 4% of world population yet have 20% of world covid deaths, Trump's failed response to the covid pandemic.
Biden put in place the requirement that anyone entering the US must go into quarantine for 10 days, seems that was not happening under Trump so US citizens flying in from some of the worst covid countries were out and about spreading the covid wow
Only have to look at how we got covid under control, anyone flying in to Oz goes into 14 days isolation and we blocked people from travelling interstate. Some rather simple measures the US could have taken but they didn't
