The UFC isn't having a banner week with a lot of drama and changes surrounding Saturday's event. The Swedish fighter got into a verbal altercation with the Brazilian on Wednesday before throwing hands. He got into a fight with Kevin Holland at the press conference.
Fight camps specialize in weeks on opponents' tendencies and how to stop specific fighting styles, so it's unusual to switch an entire card the day before a fight.
Chimaev was supposed to fight in the UFC's main event, the last fight on a current UFC contract, but the fight was canceled. If he doesn't compete on Saturday, he will be a free agent after this weekend, so it's not clear what will happen. There was a proposal to change the card. There are no official changes to the show yet, but there are some changes that would make the show better.
The news conference where Chimaev fought Holland was canceled, the second such occurrence this week. Punk insulted several AEW wrestlers at a post-show scrum and got into a backstage brawl with other members of the locker room. The CEO suspended everyone involved in the fight. The proposed changes to Saturday's UFC card haven't been announced by the company.
Chimaev is considered to be a rising star in the UFC, and was a -1000 favorite to win the fight. Chimaev was booked against a departing former star in order to build his profile. Chimaev shrugged his shoulders when he came in at 178.6 pounds. There is a limit on the UFC.