Why "New Heavens"

You may or may not have heard 17 "Behold, I will create new heavens and a new earth. (Isa 65:17) Q: why "new heavens"

We can all pretty well understand why a "new earth", but "new heavens"...?

Ever wondered what God's long-term plan for man would have been had Adam & Eve obeyed and NOT eaten of the tree of the knowledge of good and evil and HAD eaten from the tree of life and had never died?

The Amplified Bible has a footnote for Isaiah 65:17 stating: "A new universe is here meant. The Hebrew has no single word to express the thought of cosmos, so heavens and earth are substituted." So, a new heavens and earth means a New Universe. But why?

Given the very little we know of the cosmos, would we even know what a new universe would look like?

In studying scripture, seeking to understand our future state of being, after this life and what it will be like for those who remain in the body, I've come to what I believe to be some very interesting conclusions.
1. Not all believers will quote: "Go to heaven"
2. Though "...as it is appointed unto men once to die, but after this the judgment" (Heb 9:27) Not ALL will die, AND not all who will not die are necessarily "Believers".
3. Not only will there be those in physical bodies after this age, but also into eternity! (?)
4. That there are four (4) distinct groups of people upon the earth during what the Bible calls the Great Tribulation.