That was Satan's gift to mankind. I admit not many seemed to be in touch with God during the time before the flood but word about 'this one true God' has always been known. Fallen Angels would have been what 'all the others' would have been interacting with.God provided the playing field (Earth) and all its obstacles (Desires of the flesh) in the playing field.
But on top of that He gave us and element of a spiritual desire that causes us to seek out Him with whatever knowledge we have at the time.
Does spiritual mean 'by thought alone'?Consider the sorts of gods created by mankind for worship and adoration throughout its history and you will see that there lies a desire for the spiritual within each soul.
This points to physical beings,
Ge:6:1:
And it came to pass,
when men began to multiply on the face of the earth,
and daughters were born unto them,
Ge:6:2:
That the sons of God saw the daughters of men that they were fair;
and they took them wives of all which they chose.
Jude covers what they were doing
How much knowledge is God allowed (% of people) to give without it becoming under the dominion of being part of the kingdom of Heaven. So far it only seems like He needs a few to be able to save the whole. It only gets taken from Satan at a certain point, at the time the blessed hope is made manifest.But knowledge of God was not always available to mankind, so mankind adapted to a god with what ever knowledge was available at those times.
The problem with all of that, is that mankind is not to blame until....... the knowledge of the real God is made available to us.
If the numbers were reversed for who lived and died in the flood that would mean Satan had control over 8 people, the rest would have all been on 'arks'. Could Satan be called 'ruler'?