Because it’s mass produced consumer goods operating on a “below x temperature turn on heat/turn off AC” and “above y temperature turn off heat/turn on AC”. Old ones are just bimetallic strips where you change the trigger position with a slider, and modern ones use commodity grade temperature sensors, and neither is guaranteed to be placed particularly far from the vent.
Because it’s mass produced consumer goods operating on a “below x temperature turn on heat/turn off AC” and “above y temperature turn off heat/turn on AC”. Old ones are just bimetallic strips where you change the trigger position with a slider, and modern ones use commodity grade temperature sensors, and neither is guaranteed to be placed particularly far from the vent.