indeed why? it seems that the answer is too much obvious for those who are really into 3D modelling: because it's free, and only because it's free, as it seems that Blender is not yet better then other similar tools on anything, but it does everything that you need (modeling, rigging, animation, rendering, composing, etc.) and it is cross-platform (!).

Anyway, for noob starters, as myself, it has more than i can handle. After 14 hours of Blender training i manage to make a somewhat simple house and a chess piece (and i am quite happy with that!):

Kudos for Pedro Amado, the guy who teached me how to do this.