The U.S. can get close allies like UK, Australia and Canada to antagonize China simply because the U.S. has tremendous influence other those 3 countries. All 3 countries have already forgone their own interests and suffered economic bloodshed to antagonize China for the U.S.'s benefit. As of right now, it's harder for the U.S. to convince second tier allies like Germany, France, SK and Japan to forego their economic interests and follow the same path.
The reason for UK/Canada/Australia is because maintaining good relations with the U.S. is more important than maintaining good relations with China. For example, 70%+ of Canada's exports are to the U.S., so if countries like Canada and Australia don't do what the U.S. wants, the implications are worse than any Chinese retaliation.
Current governments of the Quad don't like Trump's administration, especially if U.S. actions are hurting economic interests, but since they are caught in the crossfire, they will still appease the U.S. in the meantime but are hoping for a Biden administration.
The rhetoric of the U.S. has recently changed after COVID, where the Trump administration is now calling for a "united front" against China because the U.S. wants to dilute any potential economic fallout, basically spreading the pain. IMO current U.S. hostilities against China are designed to provoke a strong Chinese response, especially one that would hurt interests of neutral countries, so the U.S. can further justify action against China.
