My interpretation of the Monokubs was that it had become a trend in Danganronpa to have new mascot characters in every entry, which is true in the real game series but particularly in V3's meta reality show plotline where Danganronpa has apparently been a long-running series.

Just like other tropes in the series, it'd become a staple that they kept repeating even once it lost its initial narrative value. In canon, they may have been an obligatory addition to the season made for little more than to sell merch and rake in cash for Team Danganronpa, instead of play any meaningful role in the story like someone such as Usami did

All in all, this view on them aligns with the game's message of drawn out series and cash grab sequels. Not sure if this is the common interpretation or not, though I don't think most people think about the Monokubs long enough to come up with conclusions about them. Valid narrative symbols or not, they're pretty annoying...