The Bible is filled with metaphors, aphorisms, parables, and other great symbols that aren't necessarily absorbed into our minds upon the first reading of it. In the beginning was the Word, but within this beginning, mankind disobeyed to his own destruction God's instruction not to partake of the tree of knowledge. Having partaken of this forbidden fruit, mankind brought upon itself the awesome knowledge of whom he really was on this material plane, but without the attendant wisdom mandated to render correct and good judgments. Man's eyes were now open to recognize that he was yet indeed a child of the great God, but somehow too, he was entrapped within a physical body which had physical sensations that were at odds to his spiritual nature and served to sever the direct ties to God himself. Placed within this position, mankind soon found out that being a mini-god with the ability and the knowledge to take actions and to make decisions on this planet, made him somewhat of a master of himself and this world. However, once encased within this world, mankind was destined to suffer the laws of physicality, of pleasure but also of pain, of joy but also of sadness, of life but also of physical death, and through it all he lost sight of whom he really was, and came to often to believe that this world was all that ever was.
However, Noah was a righteous man, blameless in the sight of God, unlike the vast majority of human beings which had become corrupt and degenerative, to which it was their evil and selfish actions that inevitably led to the destruction of their lands on earth, because a people that will not look for salvation from He who knows the number of the very hairs on your head, is a people that even God cannot save from its own demise. The flood did come not because of God's divine punishment upon a wicked people, but to demonstrate that those that turn their back on their Lord, in fact, believe that they themselves are gods of a certain sort, that they know best, and that they can do anything without consequences, are in error, because man's conscious separation from its Creator, is a law that can only end in darkness.
Those that entered upon Noah's Ark were the true believers of God, tested and true to His word. Noah's Ark would not have been necessary had mankind remained faithful and true to their Lord, but in absence of this, a baptismal cleansing of earth was mandated. Noah and his descendants represent the great hope of mankind, the opportunity to be cognizant of who we really are, and thereby to live to that knowledge, ultimately becoming one once again with our Lord.
There was never going to be just one Eden, because when mankind ate of the forbidden fruit, so that he could have free will and thereby to challenge God's authority, a never-ending cycle commenced, to which no matter how long the process takes, in the end, it cannot be other than what it always was going to be, that is to say, the wayward child will return to the fold, because in the darkness of ignorance, there is no light.