The main reason is capitalists say communism will inevitably fail and then spend billions of dollars fighting it. The war mentality makes it easy for people like Stalin to take power.

Another is few things succeed when they're first tried.

And then there are people who say individualism is the aim of capitalism, but what we end up with is an ever-growing wealth gap.

The people who benefit from a system always love it. The people who don't get ignored. That's why nostalgia for the USSR and the GDR is not noticed in the US--poor people don't matter here.