Whatever else it is, a legislature or parliamentary election is a hiring process: we have a number of candidates vying for a job on offer and presenting themselves to a selection board or board of directors (the voters), to make their respective cases; the candidates identify themselves and their views, skills, and qualifications, answer questions, and speak to why they are the best choice for the job, and how their judgement and energy will duly serve the best interests of the organization (electoral district/country).
Each board (voters, per electoral district) then makes its decision (the election), the candidate of their choice is duly hired, and then works (ideally) in the best interests of the organization (electoral district/country) as a whole — according to his or her best judgement and skills, but nevertheless with on-going feedback (whether it’s heard or not) from the board (voters). If the board (voters) aren’t satisfied with the chosen candidate’s performance, they will perhaps make a different choice when that candidate’s term is up for review (next election).
In a hiring situation having a single job on offer, if half of the board decided on one candidate, a third on another, and a sixth on yet another, we would still expect them to hire just one candidate, however the board might resolve their differences, and expect that upon being hired that candidate would then, nevertheless, work in the best interests of the organization as a whole, despite not being the first choice of every member of the board.
We would not expect them to hire half of one candidate, and a third of another, and a sixth of yet another, nor would they increase the number of job openings to six so that they could hire half the candidates from one firm, and a third from another, and a sixth from a yet another, to keep everyone on the board “happy.”
Similarly, it is hard to see a basis upon which the relative proportions of the votes for any given party, when considered for a given electoral district or even for any number of electoral districts, should necessarily translate into electing that percentage of candidates of the given party.