God could forcibly prevent people from sinning, but that would not enable us to achieve the potential that He desires for us to achieve. His will is that we learn right from wrong and that we choose to do right without pressure from Him (Deuteronomy 30:19; Amos 5:14; Acts 3:19; Romans 12:2). We must have free will to make those choices; otherwise, we will not develop godly character (Romans 5:3-4).
By analogy, people do not break the law when the police are watching. Does that prove that they are good citizens? No, for they are under pressure to comply with the law. We demonstrate good character by obeying the laws of the land when no authority is standing over us. It's similar spiritually. God makes His laws known to us, but leaves it up to us to act on that knowledge.
Working with us in this way requires infinite patience on God's part. Like a wise parent, He realizes that we need the freedom to make mistakes. By analogy, wise parents allow children in their teenage years to make and learn from mistakes, realizing that it is the only way they will learn and develop good character. Of course, parents still give their children guidance, comfort and help; but parents don't control every aspect of their children's lives. If parents are unwise and too controlling, their children never develop the maturity they need to manage their own lives.
Likewise, God does not control our every action. He allows us the freedom to obey—or to sin. God also allowed Satan to be active in this present world, playing upon the weaknesses of human nature and tempting people to make wrong choices (Ephesians 6:11-12; 1 Peter 5:8). All of these factors serve to strengthen us spiritually, for we grow in strength by resisting the forces of evil.
Has God left us to suffer the consequences of sin without any hope? No, He hasn't. He provided us with a way to obtain forgiveness for sin, through repentance and accepting the sacrifice of His Son, Jesus Christ (Acts 2:38). His plan enables us to develop genuine character at the same time as it provides us with a way to escape the death penalty that sin brings on (Romans 6:23).