They should remove Seattle's entry here. The Pronto network was cancelled in March due to disuse. https://www.citylab.com/transportation/2017/01/seattle-bike-...
Seattle has a mandatory helmet law. Are there any successful bike shares in places with helmet laws?
As far as my experience goes, the country did try heavily enforcing the helmet law when they first introduced it (about a decade ago), now it seems to me like the police simply doesn't care if you're wearing a helmet or not.
Of course, if you commit any other traffic violation on a bike, you can be pretty damn sure that they're gonna bundle it with "not wearing a helmet" fine.
[1] I live within a walking distance from the place I work in, so there's no need for me to use one every day.