Also Chromium and mozilla-central are monorepos, servo/servo is only part of all the Servo code. There are a bunch of other repos under servo/. We also rely on some major Rust libraries like hyper, but those could be excluded.
The libraries under github.com/servo are just Servo components (some of them are used by other people, though) which are in different repos. These are maintained by the Servo team and in many cases Servo-specific, for example our HTML parser, CSS parser, URL library, and our layers/geometry logic. Also, eventually, most of our rendering logic.