Why hasn't God destroyed him?
You asked the million dollar question no preacher can ever answer, it's because they don't grasp who the adversary is as they are the 1/3 fallen with the deception.
Actually it's not to hard to figure out when you study the pattern of Rome and how they conquered and controlled kingdoms and cultures. Always setting themselves up as new authority & new temple to the people's deities.
Rome was the adversary at the time of the writings, thus being warned about by John of Patmos as the one world religion ploy occuring in his time not a later time.
Motive: Their expansion was being met with resistance, &revolts were taking place against their authority and taxes. For Rome to make kingdoms submit to their whims and authority and to collect money from them they had to now cleverly hide the Political power behind the mask of religious authority with cultural familiar masks thus converged deities and mythologies pleasing each culture they ruled over. This is called the two horn (power) system, which is why the symbolism of the devil is the scarlet (color of Rome) with two horns (powers) both political hidden behind it's religious authority. Now Rome could stick it's feet in many kingdoms like warned, and be unsuspected nor challenged, while also collected taxes without revolt in the form of tithes to the cultures gods. Collecting money for salvation and homage to their deities when that money was lifting high Romes power and authority as the real god of this world speaking ehind the mask of the one world religious image named Jesus.
One of the charachters used for the Jesus image had warned, they will "come in my name" (meaning his name) and say I am christ (saying HE IS Christ-not they are) and deceive many. Throuout the NT they speak of son of man third person tense as another future person not that he is son of man. Rome the adversary created his image using many christ figures and mythical deities to draw Jews and other cultures to this new religion under their control. Baal worship given new name and mask to get revolting Jews to worship Baal under he guise of fulfilled prophecy. Meanwhile all that as fulfilled was the warning of this perfect image of man representing the fallen one aka Lucifer.
So now think as to why Lucifer is allowed to exist:
If you didn't have Lucifer (Jesus) compiling some Judaic teachings in the fold and ABRAHAM'S lessons of love for they neighbor and good deeds and other Torah Ethos then civilization would have still been following Mithra or Baal (which are portions of Lucifer's (Jesus') image. At least they become halfway home.
The bible says they will come to the Jews as seen today, and that the 2 sticks will come together as one.
You need to understand the 2 messiahs story and recognize the 2 cherubs on the ark of the covenant as representing the 2 guardians
Moshiach ben joseph the failed fallen one then Moshiach
ben David the Triumphant arch strategist.
That story even sits in the legend of the name of the holy city, the city alone is like a cliff note to the whole process so even if you were to destroy all bible references you'd still know the morning star (Lucifer Jesus) people will be over turned by the Evening Star people (those of the Liberator/redeemer/restorer).
This is why Lucifer is allowed to exist, in order to bring people half way to Torah, see what life is without the Shiloh, then find their full way grafted into Their Judaic roots thus fully Teshuva and find their peace and purpose.
If Christians scoff at becoming Jewish then they lose, because in order for Jesus to be Messiah it's required they come to the Torah(in Matt it commands also).
In order for Bible to be validated which they need for their arguments then Christians have to take hold off the garb of a Jew/ Rabbi snd ask us about our ideology (define)on God (source and power of life). They(the gentile) also have not yet seen the face of God according to
Isaiah 66:19, and they have to bring themselves into Judaism (2 sticks into 1).