It's not about rent so much as density. Seattle has this "urban village" concept where designated areas have zoning that allows apartment buildings and usually has a commercial strip. I'd guess the urban village map [1] overlaps the 15-minute zones pretty closely.
Outside of the urban villages, Seattle is comprised of neighborhoods of single-family homes. Those areas can't all be 15-minute walkable because catchement areas don't have the population needed to support those amenities.
But it's also certainly a class issue. The people walking to the grocery store are mainly the poor, students, and a small core of idealists who go out of their way to live a "city lifestyle". Everybody else drives everywhere. Which has a strange effect that wealthier neighborhoods are less likely to have things like a pharmacy, because the wealthier are in the habit of driving everywhere. I get my prescriptions filled at Costco, five miles from my house, even though the closest pharmacy is one mile.
Outside of the urban villages, Seattle is comprised of neighborhoods of single-family homes. Those areas can't all be 15-minute walkable because catchement areas don't have the population needed to support those amenities.
But it's also certainly a class issue. The people walking to the grocery store are mainly the poor, students, and a small core of idealists who go out of their way to live a "city lifestyle". Everybody else drives everywhere. Which has a strange effect that wealthier neighborhoods are less likely to have things like a pharmacy, because the wealthier are in the habit of driving everywhere. I get my prescriptions filled at Costco, five miles from my house, even though the closest pharmacy is one mile.
[1] https://i.pinimg.com/736x/87/cd/9f/87cd9ffd44c33154445747de3...