Devices usually don’t monitor for battery bulging and warn of the fire hazard. Maybe this feature is intentionally omitted to increase deaths for people who don’t replace the devices frequently enough, which is poor people and people who have a low consumption level that corporations don’t like.
More likely it’s something you can see and feel when using the device, so a sensor is an unnecessary component that can break or cause false alarms. Plus, people will wuestion why the manufacturer felt the need to install it.
You underestimate the ignorance of users