When the religion of the Veda knows no idols then why so many gods and goddesses with different form and name are being propagated as Vedic gods.

Brihadaranyaka Upanishad 1:4:8:- “This Self, which is nearer to us than anything else, is indeed dearer than a son, dearer than wealth, dearer than all beside. Let a man worship the Self alone as dear, for if he worship the Self alone as dear, the object of his love will neverperish”

 “This Self is dearer than a son, dearer than wealth, dearer than everything else, and is innermost. Should a person (holding the Self as dear) say to one calling anything else dearer than the Self, ‘(what you hold) dear will die’–he is certainly competent (to say so)–it will indeed come true. One should meditate upon the Self alone as dear. Of him who meditatesupon the Self alone as dear, the dear ones are not mortal.”

The Self is ever nearer to us than anything else. Therefore we need not reach outward for It, but turn inward to find (perceive) It. It is dearest of all to us because It IS us, and is all thatwe can ever have–everything else in all the worlds are illusions which will perish. So it certainly is truth that those who turn from the Self to outer things will find that they all die and are lost to them. For this reason it is not just noble to cherish the Self alone, it is only good sense. In fact, any other attitude is a form of insanity. By living intent on the immortal we can rise above mortality.

The Self is indeed Brahman, but through ignorance people identify it with intellect, mind, senses, passions, and the elements of earth, water, air, space, and fire. This is why the Self is said to consist of this and that, and appears to be everything. - Brihadaranyaka Upanishad

That is why Swami Vivekananda:-

The masses in India cry to sixty million gods, and still die like dogs. Where are these gods?

 Knowing this, stand up and fight! Not one step back that is the idea. ... Fight it out, whatever comes. Let the stars move from the sphere! Let the whole world stand against us! Death means only a change of garment. What of it? Thus fight! You gain nothing by becoming cowards. ... Taking a step backward, you do not avoid any misfortune. You have cried to all the gods in the world. Has misery ceased? The masses in India cry to sixty million gods, and still die like dogs. Where are these gods? ... The gods come to help you when you have succeeded. So what is the use? Die game. ... This bending the knee to superstitions, this selling yourself to your own mind does not befit you, my soul. You are infinite, deathless, birthless. Because you are infinite spirit, it does not befit you to be a slave. ... Arise! Awake! Stand up and fight! Die if you must. There is none to help you. You are the entire world. Who can help you? - Swami Vivekananda 

(Delivered In San Francisco, on May 28, 1900) -The Complete Works of Swami Vivekananda/Volume 1/Lectures And Discourses/The Gita II

The Hindus believed in polytheism, believing all of their Gods to be separate individuals, which were introduced much later by the founders of Hinduism which contains diverse beliefs caste and creed. 

When the religion of the Veda knows no idols then why so many gods and goddesses with different form and name are being propagated as Vedic gods. Why these conceptual gods are introduced when the Vedic concept of God is free from form and attributes.

Who introduced the concept of God with attributes and attributeless gods, when Yajur Veda says: -   those who worship visible things, born of the prakrti, such as the earth, trees, bodies (human and the like), in place of God are enveloped in still greater darkness. Therefore, all these add-ons proves that the form and attribute based concepts are introduced by some sages of the past with a new belief system and code of conducts in the name of Vedas. 

It clearly indicates that: -If the human goal is to acquire Self-Knowledge or Brahma Gnana or Atma Gnana then why one has to indulge in rituals and glorifying the conceptual gods and goddesses to go into deeper darkness. Instead   spend that time moving forward towards Self-knowledge, which is one’s prime goal.