Strictly speaking, it’s a wagon, with a band on it, made popular in the circus entertainment business. I imagine going round a circus ring on a wagon was preferable to walking round during the days when performing animals were still the norm.
Later the political circus ring took on the use of a band wagon to advertise a particular candidate, I’m sure well known Internet search engines could even be used to find out the name of the candidate. But it was this use of the bandwagon gave us the memorable phrase "Jumping on the Bandwagon" used when a particular candidate was seen to be popular and it wouldn’t hurt a persons own credentials to be see on the same bandwagon.
Of course jumping on the right bandwagon is important, but it’s always easier to use someone else’s wagon than build your own, buy the instruments, audition the band, write the music, decide the playlist, pay the band. Of course you may not always like the tunes you hear, you may not always be able to join in at the same speed and you’ll never know what’s coming next. But that’s the price you pay for riding on the other guys wagon.
All this talk of bandwagons and I never mentioned UTM once.