Why does Anna Karenina open with a line about Levin's brother instead of Anna?

The novel is named after Anna, but the opening chapters spend a long time with Stiva, Dolly, and Levin before Anna even appears. Tolstoy seems to be building the "unhappy family" theme first as a wide lens, then narrowing into Anna's story specifically.

Anyone else find the structure unusual on a first read? Did it change how you saw Anna once she showed up?