Partly due to a slow response by our government. Remember Trump saying it was nothing and would be all over in two weeks? However, lots of governments fumbled the ball on the response and still are (Mexico is a current hot spot as is India and much of South America).
US, 2.3 million cases, about 0.7% of the population
Brazil, 1.1 million cases, about 0.5% of the population
Russia, 0.6 million cases, about 0.4% of the population (I've seen lots of questions on other sites how truthful they are being, not that the Russians have a habit of lying about embarrassing issues).
India, 0.45 million cases, about 0.03% of the population (but they are just getting going)
UK, 0.3 million cases, about 0.45% of the population
Peru, about 0.26 million cases, about 0.8% of the population
Chile, about 0.25 million cases, about 1.3% of the population
Spain, about 0.25 million cases, about 0.5% of the population
Italy, about 0.24 million cases, about 0.4% of the population
Numbers taken from https://gisanddata.maps.arcgis.com/apps/opsdashboard/index.html#/bda7594740fd40299423467b48e9ecf6 today and of course are always changing.
Of course, they are also many countries with much, much lower % of cases because of the actions they took.