Two reasons: 1. a lot of us like having our own local copies of things (the same rational as Git, when talking a version control system). 2. a lot of use cases

Two reasons: 1. a lot of us like having our own local copies of things (the same rational as Git, when talking a version control system). 2. a lot of use cases REQUIRE a local copy, to support disconnected operations (working on airplanes, working in remote areas with poor connectivity)