Slight correction, the sales org uses GitLab, mainly to segregate any “code” they build for customers. Internal AWS/Amazon teams use an internal git-backed UI.
If AWS forced their teams to "dogfood", it would quickly morph into the Testuo blob monster from Akira -- there are too many products/services popping up too quickly, and the amount of time and knowledge lost to the constant changes would be catastrophic.
Dogfooding is for simpler companies. It's also bullshit and best for product managers and sales. Let tech work with what's best for their specific internal environment.