[worik]

Why? A wheel with less corners...

[rurban]

Some people on bigger projects are tired of waiting for their builds and test results, so they wrote something better and faster. => ninja

On bigger projects waiting 60min or 10min or 2min makes a difference.

kati so far converts traditional makefile recipes into ninja builds.

[yoklov]

Not sure this is the answer (I actually doubt it), but possibly because Make works poorly, and requires painful setup on Windows?