Why carry bear spray or a gun if you are not going to use it?
Lots of reasons.
People may carry it because someone told them they have to have it.
People often think of defensive tools as a magic talisman to ward off evil.
People believe they will have plenty of warning, and plenty of time, to access their defensive tool.
People don't rehearse possibilities. When it happens, they are caught in denial "This can't be happening!"