The same goes for GitHub and GitLab, so this isn't surprising. A real strange thing, is that one also needs a Google account to view the Android issue tracker, for instance.
In fact, that is worse. If you don't like Github and don't want a Github account, the problem is that the project you want to contribute to isn't part of Github. It's just there due to some unfortunate decision that someone made to move to Github.
If you don't like Google and don't want a Google account, you also shouldn't want to contribute to Google code; problem solved.