Replying to
@drj I thought about this a bit, and I both agree with you, but also "it's complicated", and again shows the need for a federated solution.
Firstly, most the people writing the code are on short term contracts: professors have tenure or such, but most the code is written by PhD students or RAs on short fixed term contracts. Once they're done, if it's in a university gitlab instance, they will no longer be able to contribute.
Similarly, if I'm on a project that is across institutions, then it'll be unlikely my collaborators can get an account on my university's gitlab (we do have one), and vice versa, so we're pushed to use somewhere that we can all access.
That isn't to say you're wrong, far from it, but more that there are other institutional barriers in the way, and a federated git thingy would make it a lot more credible.
That's not to say we couldn't archive things to our institution gitlab, but that feels like a place projects will go to be forgotten, not to be maintained.