I was born into the US and was a liberal for most of my life. I can explicitly tell you why so many of my countrypeoples defend capitalism:

Because they have the political education of an infant. You are told from a young age by everyone you trust that communism is bad and you never EVER get told the truth. There is absolutely no grand structure for learning about politics that isn't reactionary in nature.

What's left is an infinitesimal number of people with both the requisite curiosity and social opportunity to break out of liberal thinking. Most people are ingrained and never challenged their entire lives.

The incentives for supporting capitalism and rejecting communism are powerful and alluring in this country. But it is not an excuse. The books are out there. You absolutely must read.