In the 80s and 90s, I can recall discussions my mother had with other JWs about demons and demonic presences and even actual attacks. She would tell stories of such experiences that she had been told about. Once I got out, I noticed that all of those stories were third/fourth-hand tales. I don't recall a single person explaining something that they dealt with directly; it was always a distant relative, or a friend of a friend, and so on. But, oh boy, did we believe them!
Invisible oppressors are a convenient go-to for a lot of religious and superstitious people, as it can be used to explain stuff that otherwise would make them uncomfortable. If people of other religions are having supernatural experiences that "prove" that their faith is real, the obvious way to deal with that is to claim they are deluded. But that could also be applied to experiences that support their own beliefs. So they prefer to claim that the experiences that do not support their beliefs must have involved demons. It still leaves them open to the question of how they can be sure that they're right about who is being deceived.