In multiple verses Allah declares that He guides whomever He wants. Not that Allah needs to explain Himself; is there a verse in Quran or hadith that clearly explains the wisdom behind this? (For example, it could be that the unguided human is unguided due to his previous actions, etc.)
Alive hearts Hear the call
8:22-23 Indeed, the worst of living creatures in the sight of Allah are the deaf and dumb who do not use reason.
If Allah had found in them any good. He would indeed have made them listen: (As it is), if He had made them listen, they would but have turned back and declined (Faith).
Actions of disbelief, and disobedience would get you a sealed heart
4:155 And [We cursed them] for their breaking of the covenant and their disbelief in the signs of Allah and their killing of the prophets without right and their saying, "Our hearts are wrapped". Rather, Allah has sealed them because of their disbelief, so they believe not, except for a few.
A sealed heart, is hardened, it doesn't comprehend the message.. It is a punishment
7:179 And We have certainly created for Hell many of the jinn and mankind. They have hearts with which they do not understand, they have eyes with which they do not see, and they have ears with which they do not hear. Those are like livestock; rather, they are more astray. It is they who are the heedless.
Hardened hearts, again A Punishment!
5:13 But they broke their pledge, so We distanced them [from Us] and hardened their hearts. They distort the meaning of [revealed] words and have forgotten some of what they were told to remember: you [Prophet] will always find treachery in all but a few of them. Overlook this and pardon them: God loves those who do good.
On the contrary, a softened heart, is a bless!
6:125 So whoever Allah wants to guide - He expands his breast to [contain] Islam; and whoever He wants to misguide - He makes his breast tight and constricted as though he were climbing into the sky. Thus does Allah place defilement upon those who do not believe.
Allah can! The wisdom is: To be guided is an option! People pick, you can't impose!
10:99 And had your Lord willed, those on earth would have believed - all of them entirely. Then, [O Muhammad], would you compel the people in order that they become believers?
And Allah knows best.