Interesting how the visualization highlights the Eastlake and Montlake neighborhoods (along the south bank of the canal northeast of downtown) as walkability outliers. When I was newer to the Seattle area and looking for housing I did a similar exercise and charted the location of grocery stores. I was surprised that those neighborhoods just didn't have any grocery stores, especially given their proximity to downtown…
Montlake had a small grocery store that was torn down precisely because of the 520 construction. (I can't speak for Eastlake).
520 is a highway after all, and highways are hostile to walkability for a multitude or reasons. (this fact still remains, even though efforts are being made to improve the situation in Montlake).