Maybe a succubus/incubus would want some human sexy time
I don't particularly believe in any demons, but if one were to speculate . . . Lucifer was supposed to be cast out of heaven with a legion of his followers . . . One would assume the legion were angels and that both angels and Lucifer would have an issue with human beings.
They (humans) seemed to be favored more then the angels since God was willing to "Sacrifice" Himself to Himself to grant them grace that they may choose not to be separated from Him.
So I guess, jealousy and spite . . . Maybe good old fashion hate would be reasons "WHY" a Demon would posses a Human given the mythological "history" of these supernatural entitites.
To use as a vessel to impose its will in the physical world.
Why would a demon posses a human?Because it feels it owns the human? :) :)
Believe and Receive.
Watch what you ask for.
Demons can enter you only through sin, when you sin you open the doors for the demonic.Jesus healed a man then later told him to sin no more least something worse may come upon you.