Have you ever wondered why demonic religions have sacrifices, chanting, fasting, dedications, worship, etc.? The demons don't have the followers do it for the fun of it. This is a way that humans can be used to empower their demons to resist other humans from driving them off.
How does that work? God is a gentleman. He doesn't want to violate our free will. That includes evil humans, as well.
We Christians can kick out demons with ease, if they were just sent against someone without permission or empowerment. It is a three-second operation.
But if the demon has been given human empowerment by an occultist, there is a conflict of human wills over the disposition of that demon. If the demon has been given fasting prayers to stay in place, nothing short of fasting prayers will drive it out. Fasting is a form of sacrifice.
However, if we exercise our Christian authority to bind & loose to break the (human power given by) sacrifices, chanting, fastings, dedications and worship over the demons, they are left standing there without any cover. It becomes a three-second operation to drive them off.
If the demons have been given permission to stay by the infested person, though, they may go away -- but they will be back any time they want. Salvation, repentance and renunciation are still required to keep them away permanently. If the person refuses, we need to pray for the person to have a change of heart.
Good intentions can be a problem here. If you knock back all the demons on someone who is occultly influenced, there is no motivation to repent & renounce. It would be temporary, anyway. If you don't, the demons may be keeping them from hearing the gospel message of salvation & freedom. Thus deliverance should be done as part of ministering salvation.