To jump on the bandwagon is to join something only because it has become popular. Everybody jumped on the bandwagon, quick to jump on the bandwagon, jump on the bandwagon late.
It is always an accusation of following rather than believing. The phrase comes from American parades, where the musicians rode a wagon and politicians would jump on the bandwagon to be seen with a winner.
1phrasejump on the bandwagonTo join something only because it has become popular.
“When the diet became popular, every celebrity seemed to jump on the bandwagon.”
jump on the bandwagon is a following.
From the American bandwagon that carried musicians at the head of a parade, which politicians rode to be seen with a winner.
US 1899. A bandwagon carried the musicians at the head of a parade or at a political rally, beckoning others to follow. When used to refer to politics, jumping on the bandwagon suggests following the crowd for the excitement of the event rather than any firm conviction in its direction or truthfulness. The phrase is first attested in a letter by Theodore Roosevelt in 1899:
Etymology from Wiktionary, CC BY-SA
Practised in Idioms