When Seattle launched the bike master plan in 2007, the bicycle network was disconnected and sparse. In the first few years of the plan, sharrows---markings on the road to let drivers know that bicyclists may be present (and tell bicyclists where to ride)---were the main tool to fill in the network. While this approach may have helped to increase bicycling along many of the city's corridors, it has probably excluded a number of potential new riders, especially on roads with more traffic and higher speed limits.
Basically, sharrows are fine for people like me who are in decent shape and are relatively confident riding in traffic. But people like me are only a tiny fraction of the people who want to ride. There are a lot of people who want to ride their bikes to where they need to go but don't because they just don't feel safe in traffic.
Since 2007, thinking in the US around what it takes to encourage a broader, more inclusive spectrum of people to bicycle has evolved dramatically. This evolution is rooted in experiences from cities around the world, where investments in world-class bicycling infrastructure have contributed to significant increases in bicycling. It's also rooted in surveys and research, which have indicated that people want bicycling infrastructure that's located on low-volume, low-speed routes, or separated entirely from car traffic.
Cities across America have embraced this evolution, recognizing that high-quality bicycling infrastructure will lead more people to choose to ride, and ultimately, contribute to the future well-being of the city.
Yes, Seattle has made progress. More and more people are biking every year and the city continues to add new miles of bicycle infrastructure. But as we look around the country, we find that other cities are significantly outpacing Seattle in their efforts to transform their cities through bicycling and embracing an evolution toward a future city that is bikeable and livable, rather than one that furthers the status quo.