Because the crowd believes Paul and Barnabas to be the Greek gods in human form, and because they want to avoid any kind of judgment, they do their best to honour Paul and Barnabas. A bull was an expensive sacrifice and the wreaths would be worn on the heads of the people who participate in the procession.1
13 And the priest of Zeus, whose temple was at the entrance to the city, brought oxen and garlands to the gates and wanted to offer sacrifice with the crowds.