I recently started following mediawiki/extensions/Wikibase on Gerrit, and quite astonishingly found that nearly all of the 100 most recently updated changes appear to be owned by WMDE employees (exceptions being one change by Legoktm and some from L10n-bot). This is not the case, for example, with mediawiki/core.
While this may be desired by the Wikidata team for corporate reasons, I feel that encouraging code review by volunteers would empower both Wikidata and third-party communities with new ways of contributing to the project and raise awareness of the development team's goals in the long term.
The messy naming conventions play a role too, i.e. Extension:Wikibase is supposed to host technical documentation but instead redirects to the Wikibase portal, with actual documentation split into Extension:Wikibase Repository and Extension:Wikibase Client, apparently ignoring the fact that the code is actually developed in a single repository (correct me if I'm wrong). Just to add some more confusion, there's also Extension:Wikidata build with no documentation.
And what about wmde on GitHub with countless creatively-named repos? They make life even harder for potential contributors.
Finally, the ever-changing client-side APIs make gadgets development a pain in the ass.
Sorry if this sounds like a slap in the face, but it had to be said.