Github dislikes email “aliases” so much that they will shadow ban your otherwise normal activities for months, and once flagged, support will request not only a “valid” email domain but also that you remove the “alias” email from the account completely.
I mean more about the features that forges provide, not just a WUI for browsing code. Namely: tracking hundreds of issues, PRs, etc
There are several independent options for all of those that, while they suck to go to a different site, often do a much better job than the code forge—think how Gerrit makes PRs look foolish, Bugzilla, Trac, Trello, etc. even the humble mailing list. What’s also important to note is a separate servdce offers different (or even better) organization options. Say you wanted a “polyrepo”… well, new you need a separate issues/review for every repository which often doesn’t fit as concerns can apply to mulitple repos (which now that I think about it might be one of those pressures on folks to create monorepos due to tooling lock-in choices from certain forges). That’s not to say there isn’t a cost/benefit to losing the integration of a central spot or less servers to deploy, but it very well could mean that a small orchestra of independent services could better suit a project compared to opting into every feature a code forge is offering.
That is to say, the one feature you see in all code forges—even the simple ones like cgit—is the ability to browse code/commits.