Because with Christianity, particularly fundamentalist versions, they are one and the same, in speaking terms.

The religion validates the Patriarchy. As you said, the sheer repetition of it growing up makes it your reality. You don't realize you've been duped until adulthood. Then things fall as they do. Some start the long hard slog toward working their way out, others accept but nurse resentments about it toward men (conveniently) but also still enjoy what religion provides, and others embrace it, living quiet lives of desperation in the hopes for that heavenly reward. Interestingly, those last two groups usually become quite passive aggressive and manipulative.

Enough people have to believe in Patriarchy in order for it to stand because it's unnatural. It's like money. Money has power because we all agree that the abstraction of money has value. We agree to assign that perceived value to representative bits of paper, rounded metal, digits on a screen, etc.

Religion backs the abstract belief in Patriarchy.

It was the Apostle Paul, who never met the living Jesus and never learned from him or those who knew him who said wives obey your husbands. Not Jesus. Paul was a citizen of Rome.