Compared to you and me - God is omnipotent. However, if God is truly omnipotent explain:

1. Famine.
2. Disease and pestilence.
3. Drought and floods.
4. Cyclones and other natural disasters.
5. Starvation.
6. Torture and slavery.
7. Rape, murder, child molestation.
8. Central banking.
9. Accidents.

From my little understanding, I think the simplest explanation to this is freewill.
The question asked resembles, ''Why didn't GOD destroy Satan?
God is the root of all good and Satan is vice versa. God doesn't rule with power, but love..
Before the fall of Lucifer, he accused God of improper leadership, this was a challenge, and no one challenges God. But, God didn't destroy Satan, Why?

1. Because He rules with love and not power, If He destroyed Satan, it would instill fear in the angels and they would've no longer served Him with love, but with fear. God doesn't want this.
2. Because God has to prove that His leadership is the only good, and that of Satan's is worthless. And since Satan thinks God's leadership is poor, he is the only candidate to prove it. This explains all the listed disasters.

God omnipotence, will still be displayed fully, but with time. And then, the earth will be destroyed, as said by @scarletmedia. The delay is for the our salvation, which is a proof against Satan. This is one reason for our creation.
AJoining God's kingdom is by choice and not by force, and His omnipotence shall manifest, and all created being, with even an atom of evil will be subjected to eternal doom.

Synick