The scripture reads --
Matthew 24 (cf. Genesis 6:1-7; Mark 13:32-37; Luke 12:35-48)
36 But of that day and hour knoweth no [man], no, not the angels of heaven, but my Father only.
37 But as the days of Noe [were], so shall also the coming of the Son of man be.
38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark,
39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.
I am most interested in verse 39 which read, "And knew not until the flood came..." What was it that the antediluvians knew not?
I think with a few Biblical parallels this can be answered fairly. But I'd like to hear your thoughts before I influence them with my thoughts. You may have a better answer.