In theory, sure, but the reality is that "development activity" revolves around "codebase". Plenty of projects have separate bug tracker, source code control and CI system. Most people likely prefer GitHub's all-in-one solution, especially for small-medium open source projects.
And do we not see how terrible this is as a result? Hitching your tent to corporations, especially American corporations, is always an exercise in misery.
I recently had to rebuild a jira frontend from scratch just so a single jira tab didn't take down my 8gb MacBook. Support only the subset of features I actually use and it's great. Makes me hate jira even more.