We can also just look at the reasons people today still live in densely populated cities, despite big drawbacks such as the cost of housing. Proximity to jobs, universities, recreation options, grocery stores, and more. It makes perfect sense that during COVID when much of these benefits were essentially eliminated due to lockdowns, that the negatives began to outweigh the positives for many people, and so they moved away.
I don't know exactly what your idea of an anarchist utopia looks like, but if it still involves things like universities, a wide variety of available jobs, various recreational activities, etc. then I don't see why the desire for people to live in cities would change?
Also, not really related to my main point, but still: Yes throughout history we generally lived in rural communities, but this was not due to desire but necessity. For most of history small areas simply could not sustain large numbers of people, not too mention the other problems like housing and disease. But once we worked out how to sustain ourselves, we started living in larger and larger groups. It just so happens that some of these problems were solved under capitalism.