When God created the Earth for us, he gave us a whole lot of freedom. We could do anything we wanted except for the one law... don't eat of the fruit of the tree in the middle of the Garden. The whole Earth was free for us. But then we accepted the info from the serpent/devil as greater than that of God. By doing this, we made a pact with the devil that we would listen to him and obey his rules. In other words, we gave the Earth over to the ownership of the devil, at least as far as we were concerned.
If the devil had been somebody of little power, things might not be the same as they were. But check out the second half of Ezekiel 28 to see the power that God had given the devil. The devil was able, through our willing obedience of him, to effect great corruption in us at the core of our being. The result is that we no longer have any power on our own to turn from the devil.
The influence of the devil over us is so great that, if we use any of our strength to attempt to even believe in Jesus salvation on our own, we turn the Jesus salvation thing into corruption for ourselves. It is only through the working of the Holy Spirit in our hearts (our core being) that Jesus salvation can be worked in us successfully.
Since our corruption is this deep, and since we don't understand how such deep corruption works and what it does, we barely see why death is necessary for us, so that God can remake us in the New Heavens and the New Earth, where corruption can never happen again.
This whole operation is built on:
1. The gift of God to us so that we have life;
2. The various agreements we make, first with God... to have life, then with the devil to corrupt our life, and then with God again to bring us to His new gift of salvation (even though it is God Who effects this second agreement with Him, in our hearts).
None of this is as simple as you make it sound.

Sorry, if it seemed that I simplified things too much. I'm not the most knowledgeable on the subject. Don't you think that an all-knowing God knew that "we" would partake of the fruit? Couldn't that have been part of His plan? I never heard this wording before: "we made a pact with the devil that we would listen to him and obey his rules". Would you mind giving a scriptural reference for that? Maybe I just missed it. I that that there was no way for us to truly be tempted without having evil on the earth. We need opposing forces, so we can make decisions. If good is all you have, they there's no choice to make.