The word(s) "why" appears 68 time(s) in 63 verse(s) in Quran in Mohsin Khan translation.

(1) And when it is said to them (the Jews), "Believe in what Allah has sent down," they say, "We believe in what was sent down to us." And they disbelieve in that which came after it, while it is the truth confirming what is with them. Say (O Muhammad صلى الله عليه وسلم to them): "why then have you killed the Prophets of Allah aforetime, if you indeed have been believers?"

(2) And those who have no knowledge say: "why does not Allah speak to us (face to face) or why does not a sign come to us?" So said the people before them words of similar import. Their hearts are alike, We have indeed made plain the signs for people who believe with certainty.

(3) Have you not thought about the group of the Children of Israel after (the time of) Musa (Moses)? When they said to a Prophet of theirs, "Appoint for us a king and we will fight in Allah's Way." He said, "Would you then refrain from fighting, if fighting was prescribed for you?" They said, "why should we not fight in Allah's Way while we have been driven out of our homes and our children (families have been taken as captives)?" But when fighting was ordered for them, they turned away, all except a few of them. And Allah is All-Aware of the Zalimun (polytheists and wrong-doers).

(4) O people of the Scripture (Jews and Christians)! why do you dispute about Ibrahim (Abraham), while the Taurat (Torah) and the Injeel (Gospel) were not revealed till after him? Have you then no sense?

(5) Verily, you are those who have disputed about that of which you have knowledge. why do you then dispute concerning that of which you have no knowledge? It is Allah Who knows, and you know not.

(6) O people of the Scripture! (Jews and Christians): "why do you disbelieve in the Ayat of Allah, [the Verses about Prophet Muhammad صلى الله عليه وسلم present in the Taurat (Torah) and the Injeel (Gospel)] while you (yourselves) bear witness (to their truth)."

(7) O people of the Scripture (Jews and Christians): "why do you mix truth with falsehood and conceal the truth while you know?"

(8) Say: "O people of the Scripture (Jews and Christians)! why do you reject the Ayat of Allah (proofs, evidence, verses, lessons, signs, revelations, etc.) while Allah is Witness to what you do?"

(9) Say: "O people of the Scripture (Jews and Christians)! why do you stop those who have believed, from the Path of Allah, seeking to make it seem crooked, while you (yourselves) are witnesses [to Muhammad صلى الله عليه وسلم as a Messenger of Allah and Islam (Allah's religion, i.e. to worship none but Him Alone)]? And Allah is not unaware of what you do."

(10) Those (Jews) who said: "Verily, Allah has taken our promise not to believe in any Messenger unless he brings to us an offering which the fire (from heaven) shall devour." Say: "Verily, there came to you Messengers before me, with clear signs and even with what you speak of; why then did you kill them, if you are truthful?"