It could also be that the FBI simply dismisses these witnesses as out of scope. They were tasked to collect information as it relates to sexual assault, not whether or not Kavanaugh was a drunk frat boy @sshole.
It seems many are willing to corroborate the content of his character. That should be enough to disqualify him, but this process is so off the rails, who knows how it plays out at this point.
Lying about being a drunken frat boy asshole is the issue. That happened last week, not in the distant past.