IMO it was partially due to push to retina screens and limited vector authoring tools (SVG) that were available at that time (i.e. difficult to make beautiful s

IMO it was partially due to push to retina screens and limited vector authoring tools (SVG) that were available at that time (i.e. difficult to make beautiful scalable icons if your authoring tools offer you mostly single-color patches and at best some basic gradients). Not sure why are we still stuck on that horrible design paradigm though.