So what happened in every cycle then? The story is about FMC always having a miserable life in every incarnation, which means she never even got close to the Demon King in all the known reincarnations.
I'm gonna guess that the Church had trouble trying to find her in the previous lives, and that they couldn't just act in any way they wanted like here back then. Also, this might be the only reincarnation where the royalty was actually willing to help/listen to the Church, so there was no one of equal power that would get in their way. Just recently we had an evil Duke trying to kill FMC, so this definitely happened before.
In short, this (8th) reincarnation was simply the easiest one for the Church due to 1. FMC being in the capital, 2. FMC being easily recognizable and 3. Royalty is not fucked in the head which makes cooperation easier. Though, there were still definitely problems (aka the Duke).