Earlier quoted context omitted.
Gitea does not use Github because the software can't handle their load requirements, but because they started using GH before Gitea had all the features they needed. They are actively working on hosting Gitea on Gitea, with the last piece being an importer to move over all their GH data. Blender seems to have been ok manually migrating some things and abandoning other things, since they weren't likely to ever get a P…
How much traffic could they possibly have? Quite frankly either gitea has absolutely terrible scalability or something else is off here. Edit: i misread the parent comment. My bad.
Gitea performs alright. It can serve surprisingly-heavy traffic from a potato-tier VM with a SQLite backend (assuming the host network can keep up with it, anyway). Not Github-scale (but Github has... a lot of traffic, including a whole lot of write traffic) but quite a bit, and that's with basically the worst-possible hosting situation for handling high load.