The data format of Anki is a bit complicated but at least it's SQLite. I've seen a ton of shared decks and resources on ankiweb, but it's true you can't easily put them on GitHub.
(Anecdotally, Anki has seen a huge quality increase in the past couple of years.)
From an Android (AnkiDroid) perspective, it's allowed us to remove most of our code which was manually ported from the Python backend, with guaranteed 1:1 compatibility with upstream.
We've moved from being years behind upstream to being able to release in tandem with the Desktop app.
We also migrated to common screens written in Svelte, to reduce the maintenance burden of UI changes for screens with high churn (Deck Options being the primary example).