Standard Android does have the Mock Location feature. The issue is that apps can detect it and ban other OSes, which apps like location-based games are doing and are increasingly using Play Integrity's strong tier.
Most of these apps are already banning using GrapheneOS. A tiny minority are whitelisting the official builds. For user builds, they might as well turn off letting apps see Mock Location or Location Scopes is active, but we'd like official ones to not be banned.