You are forgetting how strong the vibes were as of November 2, 2020.
Dems absolutely were expected to win the Senate in 2020, with at least 51 seats in November (as in, not counting seats won in runoffs in GA).
Sara Gideon was supposed to beat Susan Collins
Cal Cunningham was supposed to beat Thom Tillis
Theresa Greenfield was supposed to beat Joni Ernst
Additionally, races in South Carolina, Kansas, and Montana were supposed to be heavily competitive, with both sides seen as having about equal chances of winning.
And after the sexting scandal, many expected Cunningham to lose
No one with any real political knowledge expected Democrats to win in SC/KS/MT
Even after the sexting scandal the consensus was that Cunningham would win.
