Keep in mind that the boosters flip around and initiate a burn to get back over land. As far as i'm aware, the core maintains a primarily ballistic trajectory and thus lands out in the ocean.
Scott Manley did a video a few years back explaining how this return profile works (and attempting to fly it in Orbiter)
And there was no way to eject the SRBs early, either. Once those lit, you were in for a ride...
The space shuttle had far more black zones in its launch profile than would have been acceptable in the Saturn program, or any manned program since.