Because it is a Baha'i teaching that demons and Satan do not exist.
Evil Spirits
As to the question of evil spirits, demons and monsters, any references made to them in the Holy Books have symbolic meaning. What is currently known among the public is but sheer superstition.
‘Abdu’l-Bahá, Lights of Guidance, p. 512
The reality underlying this is that the evil spirit, Satan or whatever is interpreted as evil, refers to the lower nature of man. This basic nature is symbolized in various ways. In man there are two expressions; One is the expression of nature, the other the expression of the spiritual realm. The world of nature is defective. Look at it clearly, casting aside all superstition and imagination... God has never created an evil spirit; all such ideas and nomenclature are symbols expressing the mere human or earthly nature of man. It is an essential condition of the soil of earth thorns, weeds and fruitless trees may grow from it. Relatively speaking, this is evil: it is simply the lower state and basic product of nature.
‘Abdu’l-Bahá: Promulgation of Universal Peace, pp. 294-295.
Regarding your question relative to the condition of those people who are described in the Gospel as being possessed of devils; this should be interpreted figuratively; devil or Satan is symbolic of evil and dark forces yielding to temptation.
Shoghi Effendi, Lights of Guidance, p. 513
In regard to your question concerning evil spirits and their influence upon souls, Shoghi Effendi wishes me to inform you that what is generally called evil spirit is a purely imaginary creation and has no reality whatever. But as to evil, there is no doubt that it exerts a very strong influence both in this world and in the next. ‘Abdu’l-Bahá in the "Some Answered Questions" gives us a thorough and true analysis of the problem of evil. You should preferably refer to that book for further explanation on that point.
Shoghi Effendi, Lights of Guidance, p. 521
In answer to those who may ask you what the stand is of your religion on the subject of demons, you can say without hesitation that the concept of Satan or the Devil as an actual being opposed to God is rejected by the Bahá’í teachings but that the term is understood by Bahá’ís to mean the promptings of self and desire and the dark side of human nature.
The Universal House of Justice, 1998 Dec 16, Traditional practices in Africa
The Bahá’í Teachings inform us that there is no independent force of evil in creation, but terms such as "devil" or Satan" are used in sacred books as symbols of the promptings of the lower nature of man.
The Universal House of Justice, 1985 Dec 02, Child Abuse, Psychology and Knowledge of Self
There are dark forces in the world today of despair and hatred and suspicion; the believers must, as the Master said, turn their backs on these and their faces to Him, confident of His help and protection.
Shoghi Effendi quoted in Hooper C. Dunbar’s “Forces of Our Time, The Dynamics of Light and Darkness”
We have been told over and over again in the Teachings that the forces of darkness attack Bahá’ís; and it is these forces which are seeking to disrupt your national body.
Shoghi Effendi quoted in Hooper C. Dunbar’s “Forces of Our Time, The Dynamics of Light and Darkness”
You should never allow the many dark thoughts and dark forces in the world today to weigh on your mind or depress you. The world is very black at present, and humanity in a very degraded condition spiritually. We must accept this fact, but not allow it to influence us. Our life is in the Cause of God, and we draw our strength from it, and the world of the Cause is the world of light.
Shoghi Effendi quoted in Hooper C. Dunbar’s “Forces of Our Time, The Dynamics of Light and Darkness”
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