[rendaw]

https://go.dev/blog/module-mirror-launch seems like a better source.

It seems to imply the reasons were optimization and to protect from disappearing dependencies. It doesn't imply that there were any hidden dangers to git.

I think it's very possible that google simply thinks speed is more important than decentralization. And for google's purposes, a google-owned cache is probably a safe enough hedge against disappearing repos (read: if you're not google you'd need to evaluate this risk yourself).

Edit: Discussion from the time here: https://news.ycombinator.com/item?id=20837753 - in that thread too people don't really know why the proxy was needed (or like, "is it really just for speed? but it isn't particularly slow right now"). One additional reason is analytics collection.