It's called apostacy, and it's been foretold.
The Apostacy happened when the Priests and Popes substituted the traditions of man for the word of God.
What’s also been foretold was the prompting by God to have his people to leave the Whore of Babylon mystery religion as described in the book of Revelation. People will be leaving to escape a Christless worship experience where religious syncretism is taught and sin is dressed up as good while that which is good is denounced as evil.
No one denomination can be broad brushed as being “the harlot”; the “harlot” is a Satanic entity or system of thought that rushes into Christless voids, seaking to ensnare the easily deluded. Some of these voids might be dead Catholic or Protestant churches and folks who hunger for God will leave them.