I know that humans in the cars are a big no-no, but what about test dummies? They aren’t organic, so they have no blood/guts to spill out in a crash. Plus, we would get to see how someone would be thrown out of a car in a collision, minus the gore. And no gore means no M-rating! To summarize Test dummies > No gore, whilst keeping realistic simulation > Rated E! > Everyone is happy!
In GTA V you can just drive around passively and only rob banks and do other bad stuff "at your own risk", but it's still rated M.
https://www.beamng.com/resources/driver-passengers-and-loads.2906/ This one has them in cars already, it allows you to enable seatbelts and turn them off too.