Simple answer: We didn't want another world war only 5 years after the last one ended. Defeating the Communist bloc would have required millions of US troops and tens of billions of dollars - at a time when the American people were only beginning to enjoy the fruits of the post-WWII economic boom. It was made worse by the fact that the USSR had acquired nukes, even if it didn't yet have the missiles to deliver them.
There was really just a 4-year-window - 1945 to 1949 - to strike the Communist alliance decisively, before we lost our monopoly on atomic weaponry. After that, the costs of defeating Communism simply outweighed whatever material benefits it would have brought us.