Why are most countries anti-communist?
They have a misconception of sovereignty. They really don't want to be controlled by another State, not necessarily their practice of government.
The question is really too vague, broad, and unsupported by data. Strictly NUMBER of countries, populations of countries, countries current leaders? Strictly "communism" or other socialist flavors?
In general, no one likes to think that they are under someone else's control. In reality, everyone is. "Anti-communism" is usually not so much a matter of social philosophy or organization as it is an identification with the major professed "communist-organized" states.
"Anti-communists" are really saying that they don't want to be governed by another state or people.
The communist world basically fell in 1991 with the dissolution of the USSR. China has altered its economic system that it is not that "communist" any more.
Communism is basically old news now. As well the communists had a bad record on civil rights and freedom as well as a very long record of killing their own citizens.
America and the capitalist system became dominant and everyone was keen to get on board. Being "anti communist" is a useful way of being pro America or pro business.