Keep in mind that they have access to internal polling that the public doesn’t get.
Remember when the national polls were showing 12 point leads for Biden and 17 point leads in Wisconsin and Biden campaign manager tweeted out a now ignored tweet that said internal polling had it “a lot closer” and it would “go down to the wire.”
Virtually no one picked up on that.
Why should internal polls be any more or any less accurate than public polls are?