It's because it's not. Literally all the cultures in which Catholicism thrives are those in which the extended family is paramount. My very large very Catholic very Indian family actively rails against the individualism of secular American culture. As do my Philipino friends who also have very close families. As do my Hispanic family and friends who also have very close families. As do my African friends who also have close extended families.

Literally the biggest group embracing individualism from my perspective are secular white people and mainstream protestants.

I'll stop now, but my church claim was only that the medieval church had a hand in changing the culture, in places which are now mostly protestant or atheist. The places which the post-reformation catholic church has thrived are indeed pretty different.

The dogma of Catholicism did not destroy the clan structure in Europe, though it was certainly used by those who did. It was the humans running the church, who had particular political objectives relevant to the time and place which are not necessarily anything like the political objectives of the people involved with the church these days.

No one here is making the argument that Catholicism cannot exist alongside close extended families, so your objection to the argument that is being made falls completely flat.

I'm struggling to think of a good source right now, sorry. But a link I've posted before looking the other way, at how the other half of the Roman empire turned out: https://www.theamericanconservative.com/articles/cousin-marr... also more recent discussion https://marginalrevolution.com/marginalrevolution/2018/01/ma...