I'm not Christian, nor am I going to tell you I've extensively studied the Bible because I'm not.
But I will say this. The reason God allowed humans to eat from the tree of knowledge instead of putting them somewhere else is because God has to give all of his creations freewill.
Its the same reason he can't just kill Satan, because he has to allow even his worst creations to have the freedom to choose their own path. It's the same reason he didn't kill Hitler, or Stalin, or Genghis Khan, or any of those people that we would call "evil" if you're hardcore Christian and genuinely think god should have done that. You can't take away someone's freewill to make bad choices. It's as simple as that.
