A few reasons: D3 has built-in components to draw small details like axes precisely, which lower the barrier to making good data graphics. Also, the feedback

A few reasons: D3 has built-in components to draw small details like axes precisely, which lower the barrier to making good data graphics. Also, the feedback loop in my experience is much tighter than with tools like Processing, R or Matlab, since you can manipulate elements directly in your browser, instead of having to compile code/generate a new raster image every time.