Because obviously, Satan is totes real and has power, but also prayer doesn't works. It is such a common pattern to see Jews behind anti-Christian movies that you'd think it is a requirement.
Just this year out of the top of my head:
The First Omen
Immaculate
Longlegs
Conclave (upcoming)
Doesn't surprises me at this point.
And yet . . . as published in one study of NDE's, some religious individuals who have NDE's do not find the God of their faith in their (supposed) brief dive into the afterlife:
“I was filled with a sense of absolute terror and of being past the help of anyone, even God.”
“I looked around me. Consciously searching for … God or some other angelic creature, but I was alone.”
“I expected the Lord to be there, but He wasn’t… I called on God and He wasn’t there. That’s what scared me.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6173534/
For the record, I believe NDE's are all in the head and do not represent external reality. But if I pretend they are real, and that those quoted above are accurate, then that would give credence to the notion that not all prayers are answered -- justifying the depiction in some films.
Of course, you're insisting that fictional works for entertainment should reflect what you imagine would happen in real life given the same circumstances. Therefore, in that vein, you (of course) think there's an agenda. Probably even a conspiracy.
Imagine if a simple prayer would defeat the evil in these films, then all is happy. Who would pay to see that?
And if prayer were demonstrably true and effective (which it isn't), films probably wouldn't bother to predict otherwise. It would be comparable to a film about a serious voyage casually depicting a flat earth when everyone knows the earth isn't flat. People would laugh it off and not pay to see such a film.