I have seen people consider the outcome is one of "candidate A wins" or "candidate B wins" (so binary). I do not fully agree, but practically it seems to be a good approximation - as in 30 years nobody reached something significant, and there was only one instance in 1872 when the 3rd candidate had more than 30% (https://en.wikipedia.org/wiki/List_of_third-party_and_indepe...)

Any of the supporters of "candidate A" or "candidate B" will have a vested interest to model it this way, because it can mean more votes for their candidate.