Context is everything. You don't operate on a broken pelvis of someone who would not survive the anaesthetic, you don't insult a man who's holding a knife to your child's throat, you don't break a rule to win a game.
Though omnipotent, God's actions are within a context - that of the theme of the Bible, which roughly states:
"Man cannot survive without God's help"
- that is what lies behind Man's going independent from God.
God could have simply wiped the early ones out and started again - but that would not have proved His contention, which was goaded by the adversary. So Man became independent, and that issue has to prove itself - God's intervention would only violate the terms. God cannot intervene until Mankind learns that it cannot survive on its own, and actually calls to Him for help - but although close, and closing, we have not yet reached that stage.
Were God to intervene in a small way - heal a famine, abate a war, remove some dictator - we would rely on it and never actually learn, and God would become a kind of on-call fixer rather than the Father He should be. Besides that, were he to intervene, then one religion / race / nation / side would claim they had received his blessing, and other sides would only fight to avoid looking small.
So until Mankind calls for help, the famines and tortures and slaughters and evil will go unabated - and we are not yet ready to make the call!
More importantly... if God were to intervene, then the adversary could claim legitimately that God broke the rules in order to win, and taint Him as ruling by cheating. Again, He could just kill the adversary, but what would that prove to the rest of creation? Any intervention will mean that we never have God as our Father - that is what's at stake; we will just have independence which we are too short-sighted to handle properly, more torture, more killings, more mess... with absolutely no prospect of things being better. Omnipotent yes, but there is a knife to our throat, and God will not put us at risk.
If you want to know hen we will call - it is the theme of the Bible and has nothing to do with religion or belief, easy to understand by believers and non-believers, and I can point you to it.