People stopped believing the Gospel, Early Church Fathers, Saints, and dogma about the fallen angels as much as they believed worldly ideologies.
Mainly the sorcerers Freud and Jung (it is easy to confirm that they had familiar spirits - especially Jung who actually wrote about it) and their “ideas” (lies and half-truths about human flesh from Satan).
This lead to people looking down on exorcists and anyone who believed Satan is real and preached on it. Most people who got possessed were labeled “mentally ill” and still are. I have seen plenty of possessed people in a psych ward. It seems more people in there are possessed than mentally ill. They talk to the spirits in most cases but not always and yes the spirits talk back. The demon doesn’t always reveal itself, though.*** Anyways, some people in the Church started spreading this myth that possession is rare*** when in reality you run into people who are possessed every day of your life. Satan even talked through St Peter, although he wasn’t fully possessed. And that is something to keep in mind. Possession is not always complete possession. Complete possession is more rare than partial possession (often called other things, but the point is a demon is in the flesh. St. Paul was possessed but God willed that so it was a little different. A demon was in his flesh, the definition of possession, but he was not being controlled by the demon. Rather, he was fighting the demon).
There is a good book by an exorcist called “Mary crushes the head of the serpent.” The DR Bible may or may not have mistranslated that, but it explains a fairly common reason that God allows people who are predestined for Heaven to become possessed.
Point is:
Rampant heresy and worldly thought led to the people who have the toughest job on the planet - exorcist priests - being belittled and marginalized in God’s own Church. This led to a decrease in exorcisms. Also, needing a psychiatrist to screen a possessed person doesn’t help considering they normally do not even believe Satan exists.
I salute you all
I salute your Guardian Angels