A fork of what? If you run your own instance you have control over most of those features and limits. You can’t fork a service because what you’re getting from a service is not just the code. It’s the cheaper economy of scale operational aspects of it. It’s much cheaper to pay a SaaS provider, than to have someone on payroll that manages an open alternative of that SaaS for you. The SaaS provider can then introduce arbitrary plans and limits all they want. Do you want to start another company that resells Gitlab hosting that competes with Gitlab.com?
Last time I looked into Gitlab CE I decided not to go with it because there is no pull mirroring outside of their Premium offering, I would consider this a limit.
Limits are not features. There are no limits on number of users, number of repos, etc. etc. However, you're fairly obviously not getting any of the features that are in the paid tiers of gitlab's own offering. It's open core[1], rather than just open source.