They did try this approach. There's big concrete flower boxes in many places to create some artificial hindrances. It hinders your vision, causes people to swerve, it's annoying to give way. And worst of all: it slows people down for 2 seconds after which they just floor it.

Honestly it's already pretty narrow and crowded here. I'm a regular driver here (duh) and it honestly feels dumb to drive faster than 30 because a cyclist can pop out of every corner. It's crazy to me that people want to, and do drive faster than that. But here we are. People suck.