1- Why is magic spread in society?
2- What are the methods of treating possession by Jinn other than reciting the Quran and supplication?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

Magic is one of the gravest major sins. The Prophet, sallallaahu ‘alayhi wa sallam, counted it among the seven destructive sins. On the authority of Abu Hurayrah the Prophet, sallallaahu ‘alayhi wa sallam, ordered them to avoid the seven destructive sins and counted Shirk (polytheism) and magic to be among them. [Al-Bukhari and Muslim].

Although it is one of the gravest major sins and the one who practices it risks becoming a disbeliever, and despite its multiple fatal harms for individuals and families, there are still many people who continue to practice magic and resort to it. They do so because of the weakness of their faith, envy, wickedness, their weak trust in Allaah The Almighty and weak reliance on Him, among many other reasons. Allaah The Almighty Says at the end of the verse which deals with magic (what means): {And the people learn what harms them and does not benefit them. But the Children of Israa’eel certainly knew that whoever purchased the magic would not have in the Hereafter any share. And wretched is that for which they sold themselves, if they only knew.} [Quran 2: 102]

Concerning your second question about the treatment of possession by Jinn, you should note that no treatment is more successful or more beneficial  than the Quran and the reported supplications. Rather, using them is the best treatment, whether they are directly recited over the patient, he recites them over himself, or they are recited over water, oil or honey and then drunk and/or the person washes himself with it.

There are other ways of treatment in which the Quran and supplications are not used, but most of these are unlawful, such as beating. However, using these ways along with reciting the Quran is useful in some difficult cases.

Allaah Knows best.