The tendency towards centrism is what robs our democracies of true choice.
Imagine a country with two main political parties. The one on the left gets the votes of everyone who is more left-wing than the party - because this is the choice that best represents their interests. Similar for the one on the right. But the one on the right is more centrist, and so has a greater proportion of the population for whom they are the most representative choice. The party on the left responds by becoming more centrist - they still pick up all the votes of those to the left of them, as although they are a worse choice than before, they're still better than voting for the other party. At the same time, they pull in a lot of new votes from people who are closer to the centre. We started from the top picture below, and have moved to the bottom picture. The 'left' is now in power. The right will respond by becoming more centrist.



I've picked yellow and purple because red and blue would be too obvious. This trend continues until the two main parties are almost indistinguishable from one another, and voters are robbed of choice. I could continue with what happens next, but will leave it there.