Even though people may not be engaged in politics mandatory voting is important. It reduces extremist politics and the constant need to be increasingly divisive. It forces regression to the mean.

In non mandatory voting systems the politicians need to motivate people to the polls. The default of the population is apathy so to generate action you appeal to the extremes who are the most likely to act. The more people you can make act the more you can get to vote for you.

But with mandatory voting the apathetic mass (who are most likely to be moderates as they don't really care but generally are reasonable educated people and don't agree with the extremist views) cast almost random votes which smoothes out the skew to the extremes non mandatory voting causes.