Cairo Graphics Lib question

Two days ago I installed freetype2 onto my Suse desktop. A dependency was cairo graphics (vector) lib. Now that I have these packages installed, my entire desktop looks like OSX.

This is a good thing, the graphics are much better. So, why is this? I did research on cairo and discovered that it improves display hardware. I’m just trying to pinpoint what makes cairo graphics look better than gtk+ or raster graphics. And why isn’t it installed by default?