When calibrated they're usually far better than that. Just they normally aren't factory calibrated because temperature sensing isn't the primary purpose of th

When calibrated they're usually far better than that. Just they normally aren't factory calibrated because temperature sensing isn't the primary purpose of the chip and calibrating temperature sensors is very expensive at scale (have fun heating up every wafer to a very precise 100C and cooling it down to -40C just to record temperature sensor output). Having said that, single point calibration is cheap to do (just calibrate at room temp) and pretty effective.