Not sure of the situation at present, but this has happened routinely for decades.
The Airlines are NOT common carriers, like trains and buses, and if they have (had anyway in years gone) a flight going with only a few pax and another flight going to the same destination an hour or two later with plenty of spare seats, of course they would cancel one of them.
Mind you they would not tell the pax that, would in the olden days blame maintenance or in more recent PC times technical requirements.
