"unlike the Shuttle or Apollo"
Are you comparing something that can work only in LEO with something that went to the Moon and back, and a ball of iron with little space even for three astronauts for a short time, with a full spaceplane able to carry heavy payloads and with two weeks operating capabilities?
It was impossible to ensure full survivability around the Moon - but with weights even the Saturn V couldn't lift. Within LEO, the Apollo had the same emergency mechanism.
Anyway, as other pointed out, if the rocket under the Sojuz blows unexpectedly, or the capsule itself fails or is damaged (as it did when a valve failed, killing the crew), there's no way to survive. Sure, the simpler and less capable a system is, less things can fail. A cannon ball has very few failure modes.