The show is actually fairly consistent that once contact has been made on a planetary scale, Starfleet no longer needs to hide from them. Back in TOS, Kirk was sent to negotiate with the Organians even though they were thought to be an outright preindustrial society. The Organians had contact and were trading with other space-faring civilizations, like the Klingons, so there simply isn't a reason to stay away. The other parts of the Prime Directive that get applied to interstellar civilizations, like not messing with their government without invitation, still apply.