I doubt the fundamental motive is power, or even choice. Scripture reveals that Satan hates God, and he hates man because God made and loves man. That hatred becomes particularly vicious in the case of the baptized, who have been grafted into Christ Himself.
Satan’s desire toward man, is likely to execute his hatred of God by drawing as many of us as he can into the infernal torments prepared for the devil and his angels. While he cannot attack God directly, he can attack those whom God loves… and we who have been weakend by sin and rebellion on our own part, are particularly easy targets.
The devil’s ultimate means to this end, is to undermine faith in Christ, thus dividing people from the only Savior who can save them from Satan’s tyranny. He has many tools to accomplish his ends, and possession is just one. Much more common are temptations to venial and mortal sin, and ultimately a cutting off of man from his Savior.
The ever-present and always efficacious counter-strike to all Satan has to employ, is faith and repentance, found in Christ’s Church through Word and Sacrament. The Christian who remains in Christ, has nothing to fear of the evil one.
Blessings to you.