There are a great many reasons as to why people choose not to follow the Quran, other than there’s no objective evidence that can be demonstrated that the Quran is anything other than a book written by a mad man.
The Quran, condones sex slavery.
[Quran (33:50) - “O Prophet! We have made lawful to thee thy wives to whom thou hast paid their dowers; and those (slaves) whom thy right hand possesses out of the prisoners of war whom Allah has assigned to thee” This is one of several personal-sounding verses “from Allah” narrated by Muhammad - in this case allowing a virtually unlimited supply of sex partners. Other Muslims are restricted to four wives, but they may also have sex with any number of slaves, following the example of their prophet.
There are many verses like those, there is nothing moral or great about owning another person. Rape is NEVER acceptable, under any circumstances, yet the Quran says it’s okay. This is sickening.
[Quran (3:151) - “Soon shall We cast terror into the hearts of the Unbelievers, for that they joined companions with Allah, for which He had sent no authority”.
So because someone doesn’t believe in something, that has never been proven true, you should terrorise them, force them through fear into believing nonsense too?
There is no justification for this whatsoever.
This verse is what’s responsible for my little sister being terrified at the Arianna Grande concert in Manchester, she’s absolutely terrified of going near any public concert because of that incident.
[Quran (4:11) - (Inheritance) “The male shall have the equal of the portion of two females” In Islam, sexism is mathematically established.
It’s disgusting how women are told be treated in the Quran, a woman is equal to a man, she cannot and should not be owned, she should be free to love and marry whoever she wants, no person has the right to force marriage or sexual intercourse on anyone. Yet the Quran says, a woman is worth less than half a man, and every woman must belong to some man. 
[Quran (7:80-84) - “…For ye practice your lusts on men in preference to women: ye are indeed a people transgressing beyond bounds… And we rained down on them a shower (of brimstone)”
This verse has lead to murder of homosexuals via stoning.
I have many Gay friends, they are amongst the nicest and most caring friends I could ever have, and I treasure them deeply, if anyone tried to harm them for the way they were born, my reaction would be an eye for an eye, there is nothing immoral about love between two consenting adults, irrationally killing another person, because of a book that has never been proven true, is an immorality.
Honestly… I could go on and on, pointing out the disgusting verses written in that foul book, but I feel my point has be adequately made, so I’ll finish with a verse from Sir Winston Churchill.
“How dreadful are the curses which Mohammedanism lays on its votaries! Besides the fanatical frenzy, which is as dangerous in a man as hydrophobia in a dog, there is this fearful fatalistic apathy. The effects are apparent in many countries, improvident habits, slovenly systems of agriculture, sluggish methods of commerce, and insecurity of property exist wherever the followers of the Prophet rule or live.” - Winston Churchill