It's important to keep in mind that medical payments coverage pays for your injuries as well. In addition, what if your passengers are your children or family members? It's unlikely that they would sue you for their injuries. Liability
is intended to provide coverage if you are sued, so technically a passenger could sue you, and if they win your liability coverage would pay out for the judgement. Liability coverage also pays for things like work loss resulting from an accident so those limits are generally much higher than medical coverage to account for additional expenses. Medical payments coverage is intended to pay for immediate medical bills.