The number one reason it was done was because somebody wants current day Americans DEAD.
With them DEAD the takeover of America is a cake walk.
With them alive the takeover takes longer.
There weren't as many sheep as first thought, apparently.
JMO, YMMV
That makes no sense since Covid was worldwide. That means a worldwide population reduction. And while population reduction does fit their agenda, It did not specifically target the US. What happened in the US was the opening of the flood gates to justify methods of cheating. Which they did.