The reason it works for churches is because the data told to churches are somewhat embarrassing for the confessor, and if leaked, will destroy the confessor's reputation (if not get into legal troubles).

The data that google collects are somewhat useless on their own, and is only valuable in aggregate with the millions of others they also collect. And for an individual, the leakage of this data (e.g., your advertising profile) is not detrimental unless the data is highly identifying (like your name, address, phone etc).

Therefore, people tend to simply ignore such leaks, and place zero value on the data. This difference in valuation is how google generates their money. The church, on the other hand, generates value from the gratitude of the confessors, and is therefore, aligned with the interest of the confessors.