> Atomization is a fact, and the best road out of it might be to connect with other like minded people wherever they are, but it seems that the Internet hasn't lived up to this promise. Why? What have we done wrong?

The Internet itself is just a way to transfer information. Humans are the ones manipulating that information for commercial and ideological reasons. I would say as several posters above have implied we have not evolved filters that protect us from this manipulation. Quite the opposite we have biases baked into us that are being actively exploited.

What we have done wrong is not find a way to manage this for the benefit of society rather than its harm, sadly that describes much of human history. When an environment exists that amplifies self serving behavior and concentration of power it is not surprising to see it come to reflect the worse rather than best of humanity.