Flippanarchy

It's a bit more complicated, and others are saying literal nonsense.

Communists views the necessity of a period of "dictatorship of the proletariat", where the workers take state power and become the dominant class, using it to advance their class interests such as discriminating against bourgeois and erasing the existing class relations, reorganizing production, actively working with and supporting communist movements abroad (without which the revolution is bound to fail as seen in USSR), etc. Centralization is a practical necessity for advancing class interests mentioned above, suppressing counter-revolutions (bourgeois don't just disappear), organizing defense against foreign capital who will attempt to commit imperialism and so on.

Now notice how it is a period where proletariat as a class wield state power and it is explicitly not communism which is a classless, stateless society. One is necessary to achieve the other, but both of these stages share very little in common given their place in history.

All that being said it's not like the ultimate goal, which is communism, would have absolutely no centralization. There would still be efficient, large-scale factories efficiently creating goods to satisfy needs for a large amount of people in contrast to anarchist vision of decentralized medieval villages that only participate in small-scale or petty production.